Identification of multiple amyloidogenic sequences in laminin-1

Amyloid fibril formation is associated with several pathologies, including Alzheimer's disease, Parkinson's disease, type II diabetes, and prion diseases. Recently, a relationship between basement membrane components and amyloid deposits has been reported. The basement membrane protein, laminin, may be involved in amyloid-related diseases, since laminin is present in amyloid plaques in Alzheimer's disease and binds to amyloid precursor protein. Recently, we showed that peptide A208 (AASIKVAVSADR), the IKVAV-containing peptide, formed amyloid-like fibrils. We previously identified 60 cell adhesive sequences in laminin-1 using a total of 673 12-mer synthetic peptides. Here, we screened for additional amyloidogenic sequences among 60 cell adhesive peptides derived from laminin-1. We first examined amyloid-like fibril formation by the 60 active peptides with Congo red, a histological dye binding to many amyloid-like proteins. Thirteen peptides were stained with Congo red. Four of the 13 peptides promoted cell attachment and neurite outgrowth like the IKVAV-containing peptide. The four peptides also showed amyloid-like fibril formation in both X-ray diffraction and electron microscopic analyses. The amyloidogenic peptides contain consensus amino acid components, including both basic and acidic amino acids and Ser and Ile residues. These results indicate that at least five laminin-derived peptides can form amyloid-like fibrils. We conclude that the laminin-derived amyloidogenic peptides have the potential to form amyloid-like fibrils in vivo, possibly when laminin-1 is degraded.     

Amyloid-like properties of a synthetic peptide corresponding to the carboxy terminus of beta-amyloid protein precursor.

A synthetic peptide whose sequence corresponds to the 20 carboxy-terminal amino acids of beta-amyloid protein precursor (APP) was found to form fibrils in vitro. These fibrils showed birefringence in polarized light when stained with Congo red, fluoresced when bound with thioflavin S, were resistant to proteases, and had a cross-beta conformation. By contrast, peptides with other sequences from the intracellular domain of APP and a peptide corresponding to this entire domain did not exhibit the full range of beta-amyloid properties. These results suggest that a fragment from the C-terminus of the beta-amyloid protein precursor could bind to intraneuronal paired helical filaments and account for some of its amyloid-like properties.     

B133 (DSITKYFQMSLE), a laminin β1-derived peptide, contains distinct core sequences for both integrin α2β1-mediated cell adhesion and amyloid-like fibril formation

The B133 peptide (DSITKYFQMSLE, mouse laminin β1 chain 1319-1330) promotes cell attachment, and forms amyloid-like fibrils. Here, we evaluated the active core sequences using B133 deletion peptides. B133a, lacking the N-terminal Asp residue, promoted cell spreading via integrin α2β1, whereas B133g, lacking the C-terminal Glu residue, lost the activity. Congo red analysis using the truncated peptides determined that B133g forms amyloid-like fibrils but B133a did not. These results suggest that the N- and C-terminal amino acids contribute to integrin α2β1 binding and to fibril formation, respectively. Further analyses using the truncated peptides showed that the C-terminal eight residues (B133d: KYFQMSLE) are a minimum active sequence for integrin α2β1-mediated cell attachment and the N-terminal nine residues (B133i: DSITKYFQM) are critical for amyloid-like fibril formation. These results suggest that peptide B133 is multifunctional with two different active core sequences: integrin α2β1-mediated cell attachment and amyloid-like fibril formation. Moreover, alanine substitution analysis of B133a indicated that six amino acids, Ile, Thr, Tyr, Phe, Met, and Glu, are important for cell attachment activity. When the Ser residue at the 9th position of B133a was replaced with Ala, the cell attachment activity was enhanced. Further mutation analysis at the 9th position of B133a using various amino acids suggests that hydrophobic amino acids are effective for the integrin α2β1-mediated cell attachment activity. These findings define multifunctional and overlapping sites on the B133 peptide and are useful for designing multifunctional synthetic molecules.     

Unwinding fibril formation of medin, the peptide of the most common form of human amyloid

Medin amyloid affects the medial layer of the thoracic aorta of most people above 50 years of age. The consequences of this amyloid are not completely known but the deposits may contribute to diseases such as thoracic aortic aneurysm and dissection or to the general diminished elasticity of blood vessels seen in elderly people. We show that the 50-amino acid residue peptide medin forms amyloid-like fibrils in vitro. With the use of Congo red staining, Thioflavin T fluorescence, electron microscopy, and a solid-phase binding assay on different synthetic peptides, we identified the last 18-19 amino acid residues to constitute the amyloid-promoting region of medin. We also demonstrate that the two C-terminal phenylalanines, previously suggested to be of importance for amyloid formation, are not required for medin amyloid formation.     

Solution conformation and amyloid-like fibril formation of a polar peptide derived from a beta-hairpin in the OspA single-layer beta-sheet

A 23-residue peptide termed BH(9-10) was designed based on a beta-hairpin segment of the single-layer beta-sheet region of Borrelia OspA protein. The peptide contains a large number of charged amino acid residues, and it does not follow the amphipathic pattern that is commonly found in natural beta-sheets. In aqueous solution, the peptide was highly soluble and flexible, with a propensity to form a non-native beta-turn. Trifluoroethanol (TFE) stabilized a native-like beta-turn in BH(9-10). TFE also decreased the level of solubility of the peptide, resulting in peptide precipitation. The precipitation process accompanied a conformational conversion to a beta-sheet structure, as judged with circular dichroism spectroscopy. The precipitate was found to be fibrils similar to those associated with human amyloid diseases. The fibrillization kinetics depended on peptide and TFE concentrations, and had a nucleation step followed by an assembly step. The fibrillization was reversible, and the dissociation reaction involved two phases. TFE appears to induce the fibrils by stabilizing a beta-sheet conformation of the peptide that optimally satisfies hydrogen bonding and electrostatic complementarity. This TFE-induced fibrillization is quite unusual, because most amyloidogenic peptides form fibrils in aqueous solution and TFE disrupts these fibrils. Nevertheless, the BH(9-10) fibrils have similar structure to other fibrils, supporting the emerging idea that polypeptides possess an intrinsic ability to form amyloid-like fibrils. The high level of solubility of BH(9-10), the ability to precisely control fibril formation and dissociation, and the high-resolution structure of the same sequence in the beta-hairpin conformation in the OspA protein provide a tractable experimental system for studying the fibril formation mechanism.     

Amyloid-forming peptides from beta2-microglobulin-Insights into the mechanism of fibril formation in vitro

Beta(2)-Microglobulin (beta(2)m) is one of over 20 proteins known to be involved in human amyloid disease. Peptides equivalent to each of the seven beta-strands of the native protein, together with an eighth peptide (corresponding to the most stable region in the amyloid precursor conformation formed at pH 3.6, that includes residues in the native strand E plus the eight succeeding residues (named peptide E')), were synthesised and their ability to form fibrils investigated. Surprisingly, only two sequences, both of which encompass the region that forms strand E in native beta(2)m, are capable of forming amyloid-like fibrils in vitro. These peptides correspond to residues 59-71 (peptide E) and 59-79 (peptide E') of intact beta(2)m. The peptides form fibrils under the acidic conditions shown previously to promote amyloid formation from the intact protein (pH <5 at low and high ionic strength), and also associate to form fibrils at neutral pH. Fibrils formed from these two peptides enhance fibrillogenesis of the intact protein. No correlation was found between secondary structure propensity, peptide length, pI or hydrophobicity and the ability of the peptides to associate into amyloid-like fibrils. However, the presence of a relatively high content of aromatic side-chains correlates with the ability of the peptides to form amyloid fibrils. On the basis of these results we propose that residues 59-71 may be important in the self-association of partially folded beta(2)m into amyloid fibrils and discuss the relevance of these results for the assembly mechanism of the intact protein in vitro.     

A partially structured region of a largely unstructured protein, Plasmodium falciparum merozoite surface protein 2 (MSP2), forms amyloid-like fibrils.

Merozoite surface protein 2 (MSP2) from the human malaria parasite Plasmodium falciparum is expressed as a GPI-anchored protein on the merozoite surface. It has been implicated in the process of erythrocyte invasion and is a leading vaccine candidate. MSP2 is an intrinsically unstructured protein (IUP), and recombinant MSP2 forms amyloid-like fibrils upon storage. We have examined synthetic peptides corresponding to sequences in the conserved N-terminal region of MSP2 for the presence of local structure and the ability to form fibrils related to those formed by full-length MSP2. In a 25-residue peptide corresponding to the entire N-terminal region of mature MSP2, structures calculated from NMR data show the presence of nascent helical and turn-like structures. An 8-residue peptide from the central region of the N-terminal domain (residues 8-15) also formed a turn-like structure. Both peptides formed fibrils that were similar but not identical to the amyloid-like fibrils formed by full-length MSP2. Notably, the fibrils formed by the peptides bound both Congo Red and Thioflavin T, whereas the fibrils formed by full-length MSP2 bound only Congo Red. The propensity of peptides from the N-terminal conserved region of MSP2 to form amyloid-like fibrils makes it likely that this region contributes to fibril formation by the full-length protein. Thus, in contrast to the more common pathway of amyloid formation by structured proteins, which proceeds via partially unfolded intermediates that then undergo beta-aggregation, MSP2 is an example of a largely unstructured protein with at least one small structured region that has an important role in fibril formation.     

Multifunctional peptide fibrils for biomedical materials

The Ile-Lys-Val-Ala-Val (IKVAV) containing peptide, A208 (AASIKVAVSADR, mouse laminin alpha1 chain 2097-2108), was recently found to form amyloid-like fibrils. Fibril formation is critical for its biological activities, including promotion of cell adhesion and neurite outgrowth. In the present study, we designed multifunctional peptide fibrils using the A208 peptide and an Arg-Gly-Asp (RGD)-containing fibronectin active sequence for biomedical applications. The fibronectin active sequence GRGDS (FN) or a scrambled sequence RSGGD (SC) were conjugated to either A208 or to A208S (AASVVIAKSADR), a scrambled peptide of A208, with a glycine as a spacer. The FN-A208 and SC-A208 peptides formed a gel and were stained with Congo red similar to that of A208, but FN-A208S and SC-A208S did not form a gel. These results indicate that FN-A208 and SC-A208 form amyloid-like fibrils similar to A208. A208 and SC-A208 promoted cell attachment with filopodia formation, and this adhesion was inhibited by the IKVAV-containing peptide, but not by EDTA or a GRGDS peptide. FN-A208 promoted cell attachment with well-organized actin stress fibers, and this adhesion was partially inhibited by either EDTA, GRGDS, or IKVAV. These data suggest that A208 binds to only IKVAV receptor(s) while the FN-A208 interacts with both integrins and the IKVAV receptor(s). We conclude that multifunctional peptide fibrils can be designed by conjugation of active peptides on A208 and that this construct has potential to serve as a bioadhesive for tissue regeneration and engineering.     

Is Congo red an amyloid-specific dye?

Congo red (CR) binding, monitored by characteristic yellow-green birefringence under crossed polarization has been used as a diagnostic test for the presence of amyloid in tissue sections for several decades. This assay is also widely used for the characterization of in vitro amyloid fibrils. In order to probe the structural specificity of Congo red binding to amyloid fibrils we have used an induced circular dichroism (CD) assay. Amyloid fibrils from insulin and the variable domain of Ig light chain demonstrate induced CD spectra upon binding to Congo red. Surprisingly, the native conformations of insulin and Ig light chain also induced Congo red circular dichroism, but with different spectral shapes than those from fibrils. In fact, a wide variety of native proteins exhibited induced CR circular dichroism indicating that CR bound to representative proteins from different classes of secondary structure such as alpha (citrate synthase), alpha + beta (lysozyme), beta (concavalin A), and parallel beta-helical proteins (pectate lyase). Partially folded intermediates of apomyoglobin induced different Congo red CD bands than the corresponding native conformation, however, no induced CD bands were observed with unfolded protein. Congo red was also found to induce oligomerization of native proteins, as demonstrated by covalent cross-linking and small angle x-ray scattering. Our data suggest that Congo red is sandwiched between two protein molecules causing protein oligomerization. The fact that Congo red binds to native, partially folded conformations and amyloid fibrils of several proteins shows that it must be used with caution as a diagnostic test for the presence of amyloid fibrils in vitro.     

Identification of a novel human islet amyloid polypeptide beta-sheet domain and factors influencing fibrillogenesis

Human islet amyloid polypeptide (hIAPP) accumulates as pancreatic amyloid in type 2 diabetes and readily forms fibrils in vitro. Investigations into the mechanism of hIAPP fibril formation have focused largely on residues 20 to 29, which are considered to comprise a primary amyloidogenic domain. In rodents, proline substitutions within this region and the subsequent beta-sheet disruption, prevents fibril formation. An additional amyloidogenic fragment within the C-terminal sequence, residues 30 to 37, has been identified recently. We have extended these observations by examining a series of overlapping peptide fragments from the human and rodent sequences. Using protein spectroscopy (CD/FTIR), electron microscopy and X-ray diffraction, a previously unrecognised amyloidogenic domain was localised within residues 8 to 20. Synthetic peptides corresponding to this region exhibited a transition from random coil to beta-sheet conformation and assembled into fibrils having a typical amyloid-like morphology. The comparable rat 8-20 sequence, which contains a single His18Arg substitution, was also capable of assembling into amyloid-like fibrils. Examination of peptide fragments corresponding to residues 1 to 13 revealed that the immediate N-terminal region is likely to have only a modulating influence on fibril formation or conformational conversion. The contributions of charged residues as they relate to the amyloid-forming 8-20 sequence were also investigated using IAPP fragments and by assessing the effects of pH and counterions. The identification of these principal amyloidogenic sequences and the effects of associated factors provide details on the IAPP aggregation pathway and structure of the peptide in its fibrillar state.     

Amyloid from a histochemical perspective. A review of the structure,properties and types of amyloid,and a proposed staining mechanism for Congo red staining

Amyloid is a diverse group of unrelated peptides or proteins that have positive functionality or are associated with various pathologies. Despite vast differences, all amyloids share several features that together uniquely define the group. 1) All amyloids possess a characteristic cross-ß pattern with X-ray diffraction typical of ß-sheet secondary protein structures. 2) All amyloids are birefringent and dichroic under polarizing microscopy after staining with Congo red, which indicates a crystalline-like (ordered) structure. 3) All amyloids cause a spectral shift in the peak wavelength of Congo red with conventional light microscopy due to perturbation of π electrons of the dye. 4) All amyloids show heightened intensity of fluorescence with Congo red, which suggests an unusual degree of packing of the dye onto the substrate. The ß portion of amyloid molecules, the only logical substrate for specific Congo red staining under histochemical conditions, consists of a stack of ß-sheets laminated by hydrophilic and hydrophobic interactions between adjacent pairs. Only the first and last ß-sheets are accessible to dyes. Each sheet is composed of numerous identical peptides running across the width of the sheet and arranged in parallel with side chains in register over the length of the fibril. Two sets of grooves are bordered by side chains. X grooves run perpendicular to the long axis of the fibril; these grooves are short (the width of the sheet) and number in the hundreds or thousands. Y grooves are parallel with the long axis. Each groove runs the entire length of the fibril, but there are very few of them. While Congo red is capable of ionic bonding with proteins via two sulfonic acid groups, physical constraints on the staining solution preclude ionic interactions. Hydrogen bonding between dye amine groups and peptide carbonyls is the most likely primary bonding mechanism, because all ß-sheets possess backbone carbonyls. Various amino acid residues may form secondary bonds to the dye via any of three van der Waals forces. It is possible that Congo red binds within the Y grooves, but that would not produce the characteristic staining features that are the diagnostic hallmarks of amyloid. Binding in the X grooves would produce a tightly packed series of dye molecules over the entire length of the fibril. This would account for the signature staining of amyloid by Congo red: dichroic birefringence, enhanced intensity of fluorescence and a shift in visible absorption wavelength.     

The molecular structure of UDP-galactose 4-epimerase from Escherichia coli determined at 2.5 A resolution.

UDP-galactose 4-epimerase catalyzes the conversion of UDP-galactose to UDP-glucose during normal galactose metabolism. The molecular structure of UDP-galactose 4-epimerase from Escherichia coli has now been solved to a nominal resolution of 2.5 A. As isolated from E. coli, the molecule is a dimer of chemically identical subunits with a total molecular weight of 79,000. Crystals of the enzyme used for this investigation were grown as a complex with the substrate analogue, UDP-benzene, and belonged to the space group P2(1)2(1)2(1) with unit cell dimensions of a = 76.3 A, b = 83.1 A, c = 132.1 A, and one dimer per asymmetric unit. An interpretable electron density map calculated to 2.5 A resolution was obtained by a combination of multiple isomorphous replacement with six heavy atom derivatives, molecular averaging, and solvent flattening. Each subunit of epimerase is divided into two domains. The larger N-terminal domain, composed of amino acid residues 1-180, shows a classic NAD+ binding motif with seven strands of parallel beta-pleated sheet flanked on either side of alpha-helices. The seventh strand of the beta-pleated sheet is contributed by amino acid residues from the smaller domain. In addition, this smaller C-terminal domain, consisting of amino acid residues 181-338, contains three strands of beta-pleated sheet, two major alpha-helices and one helical turn. The substrate analogue, UDP-benzene, binds in the cleft located between the two domains with its phenyl ring in close proximity to the nicotinamide ring of NAD+. Contrary to the extensive biochemical literature suggesting that epimerase binds only one NAD+ per functional dimer, the map clearly shows electron density for two nicotinamide cofactors binding in symmetry-related positions in the dimer. Likewise, each subunit in the dimer also binds one substrate analogue.     

A designed system for assessing how sequence affects alpha to beta conformational transitions in proteins.

The role of amino acid sequence in conformational switching observed in prions and proteins associated with amyloid diseases is not well understood. To study alpha to beta conformational transitions, we designed a series of peptides with structural duality; namely, peptides with sequence features of both an alpha-helical leucine zipper and a beta-hairpin. The parent peptide, Template-alpha, was designed to be a canonical leucine-zipper motif and was confirmed as such using circular dichroism spectroscopy and analytical ultracentrifugation. To introduce beta-structure character into the peptide, glutamine residues at sites away from the leucine-zipper dimer interface were replaced by threonine to give Template-alphaT. Unlike the parent peptide, Template-alphaT underwent a heat-inducible switch to beta-structure, which reversibly formed gels containing amyloid-like fibrils. In contrast to certain other natural proteins where destabilization of the native states facilitate transitions to amyloid, destabilization of the leucine-zipper form of Template-alphaT did not promote a transformation. Cross-linking the termini of the peptides compatible with the alternative beta-hairpin design, however, did promote the change. Furthermore, despite screening various conditions, only the internally cross-linked form of the parent, Template-alpha, peptide formed amyloid-like fibrils. These findings demonstrate that, in addition to general properties of the polypeptide backbone, specific residue placements that favor beta-structure promote amyloid formation.     

Ethanol induced the formation of β‐sheet and amyloid‐like fibrils by surfactant‐like peptide A6K

Self‐assembly of natural or designed peptides into fibrillar structures based on β‐sheet conformation is a ubiquitous and important phenomenon. Recently, organic solvents have been reported to play inductive roles in the process of conformational change and fibrillization of some proteins and peptides. In this study, we report the change of secondary structure and self‐assembling behavior of the surfactant‐like peptide A6K at different ethanol concentrations in water. Circular dichroism indicated that ethanol could induce a gradual conformational change of A6K from unordered secondary structure to β‐sheet depending upon the ethanol concentration. Dynamic light scattering and atomic force microscopy revealed that with an increase of ethanol concentration the nanostructure formed by A6K was transformed from nanosphere/string‐of‐beads to long and smooth fibrils. Furthermore, Congo red staining/binding and thioflavin‐T binding experiments showed that with increased ethanol concentration, the fibrils formed by A6K exhibited stronger amyloid fibril features. These results reveal the ability of ethanol to promote β‐sheet conformation and fibrillization of the surfactant‐like peptide, a fact that may be useful for both designing self‐assembling peptide nanomaterials and clarifying the molecular mechanism behind the formation of amyloid fibrils. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Fibrils from Designed Non-Amyloid-Related Synthetic Peptides Induce AA-Amyloidosis during Inflammation in an Animal Model

Background

Mouse AA-amyloidosis is a transmissible disease by a prion-like mechanism where amyloid fibrils act by seeding. Synthetic peptides with no amyloid relationship can assemble into amyloid-like fibrils and these may have seeding capacity for amyloid proteins.

Principal Findings

Several synthetic peptides, designed for nanotechnology, have been examined for their ability to produce fibrils with Congo red affinity and concomitant green birefringence, affinity for thioflavin S and to accelerate AA-amyloidosis in mice. It is shown that some amphiphilic fibril-forming peptides not only produced Congo red birefringence and showed affinity for thioflavin S, but they also shortened the lag phase for systemic AA-amyloidosis in mice when they were given intravenously at the time of inflammatory induction with silver nitride. Peptides, not forming amyloid-like fibrils, did not have such properties.

Conclusions

These observations should caution researchers and those who work with synthetic peptides and their derivatives to be aware of the potential health concerns.     

Amyloid Angiopathy of Alzheimer''s Disease: Amino Acid Composition and Partial Sequence of a 4,200-Dalton Peptide Isolated from Cortical Microvessels

The cardinal lesions of Alzheimer's disease are neurofibrillary tangles, senile neuritic plaques, and vascular amyloid, the latter generally involving cortical arteries and small arterioles. All three lesions are composed of amyloid-like, beta-pleated sheet fibrils. Recently, a 4,200-dalton peptide has been isolated from extraparenchymal meningeal vessels, neuritic plaques, and neurofibrillary tangles. The assumption of N-terminal homogeneity in vascular amyloid has been used as an argument for a neuronal (versus blood) origin of the peptide. However, intracortical microvessels from Alzheimer's disease have not been previously isolated. The present studies describe the isolation of a microvessel fraction from Alzheimer's disease and control fresh autopsy human brain. Alzheimer's disease isolated brain microvessels that were extensively laden with amyloid and control microvessels were solubilized in 90% formic acid and analyzed by urea sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The arteriole fraction from the Alzheimer's subject with extensive amyloid angiopathy contained a unique 4,200-dalton peptide, whereas the arterioles or capillaries isolated from two controls and two Alzheimer's disease subjects without angiopathy did not. This peptide was purified by HPLC and amino acid composition analysis showed the peptide is nearly identical to the 4,200-dalton peptide recently isolated from neuritic plaques or from neurofibrillary tangles. Sequence analysis revealed N-terminal heterogeneity. The N-terminal sequence was: Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr, which is identical to the N-terminal sequence of the 4,200-dalton peptide isolated previously from extraparenchymal meningeal vessels and neuritic plaques.(ABSTRACT TRUNCATED AT 250 WORDS)     

Escherichia coli peptide binding protein OppA has a preference for positively charged peptides

The Escherichia coli peptide binding protein OppA is an essential component of the oligopeptide transporter Opp. Based on studies on its orthologue from Salmonella typhimurium, it has been proposed that OppA binds peptides between two and five amino acids long, with no apparent sequence selectivity. Here, we studied peptide binding to E. coli OppA directly and show that the protein has an unexpected preference for basic peptides. OppA was expressed in the periplasm, where it bound to available peptides. The protein was purified in complex with tightly bound peptides. The crystal structure (up to 2.0 Å) of OppA liganded with the peptides indicated that the protein has a preference for peptides containing a lysine. Mass spectrometry analysis of the bound peptides showed that peptides between two and five amino acids long bind to the protein and indeed hinted at a preference for positively charged peptides. The preference of OppA for peptides with basic residues, in particular lysines, was corroborated by binding studies with peptides of defined sequence using isothermal titration calorimetry and intrinsic protein fluorescence titration. The protein bound tripeptides and tetrapeptides containing positively charged residues with high affinity, whereas related peptides without lysines/arginines were bound with low affinity. A structure of OppA in an open conformation in the absence of ligands was also determined to 2.0 Å, revealing that the initial binding site displays a negative surface charge, consistent with the observed preference for positively charged peptides. Taken together, E. coli OppA appears to have a preference for basic peptides.     

A synthetic peptide corresponding to the phosphorylcholine (PC)-binding region of human C-reactive protein possesses the TEPC-15 myeloma PC-idiotype.

C-reactive protein (CRP) is a major acute phase reactant in most mammalian species. CRP molecules from all species display Ca2(+)-dependent binding to phosphorylcholine (PC). The conserved PC-binding region of CRP corresponds to amino acids 51-66 within the human CRP sequence. A synthetic peptide composed of residues 47-63 of human CRP was previously shown to possess PC binding activity. The charged amino acids at positions 57, 58, 60, and 62 of this synthetic peptide were critical for PC-binding based on lower binding activity of synthetic peptides containing uncharged residues at these positions. The PC-binding peptide was used to generate mouse mAb that were tested for reactivity with intact CRP and with the TEPC-15 (T-15) mouse myeloma protein that also binds PC. The PC-binding peptide of CRP was recognized by two mAb specific for the T-15 Id. One of the mAb generated against the PC-binding peptide of CRP (IID6.2) recognized an epitope on the T-15 protein that was also recognized by the near-binding site-specific mAb (F6) to the T-15 PC-Id. Binding of IID6.2 to T-15 myeloma protein was not inhibited by PC and did not require Ca2+; however, binding was inhibited by the synthetic PC-binding peptide itself. Recognition of synthetic peptides containing uncharged amino acid substitutions by mAb F6 and IID6.2 was greatly reduced indicating that the shared epitope on T-15 and CRP was composed of similar charged residues. Therefore, CRP displays the same idiotope as an antibody that shares its specificity for the hapten, PC.     

Solid-State NMR characterization of autofluorescent fibrils formed by the elastin-derived peptide GVGVAGVG

The characterization of the molecular structure and physical properties of self-assembling peptides is an important aspect of optimizing their utility as scaffolds for biomaterials and other applications. Here we report the formation of autofluorescent fibrils by an octapeptide (GVGVAGVG) derived via a single amino acid substitution in one of the hydrophobic repeat elements of human elastin. This is the shortest and most well-defined peptide so far reported to exhibit intrinsic fluorescence in the absence of a discrete fluorophore. Structural characterization by FTIR and solid-state NMR reveals a predominantly β-sheet conformation for the peptide in the fibrils, which are likely assembled in an amyloid-like cross-β structure. Investigation of dynamics and the effects of hydration on the peptide are consistent with a rigid, water excluded structure, which has implications for the likely mechanism of intrinsic fibril fluorescence.     

FT-Raman spectroscopy as diagnostic tool of Congo red binding to amyloids

Chorion is the major component of silkmoth eggshell. More than 95% of its dry mass consists of the A and B families of low molecular weight structural proteins, which have remarkable mechanical and chemical properties protecting the oocyte and developing embryo from environmental hazards. We present data from FT-Raman spectroscopy of silkmoth chorion and amyloid-like fibrils formed from peptide analogues of chorion proteins, both unstained and stained by Congo red. The results show that FT-Raman spectroscopy is not a straightforward diagnostic tool for the specific interactions of Congo red with amyloids: a dilute aqueous solution of the Congo red dye at pH 5.5 and a thin solid film of the dye cast from this solution exhibit the same "diagnostic" Raman shifts relative to the neat Congo red dry powder as do amyloid fibrils formed from peptide analogues of chorion proteins stained by Congo red. An important consequence of this finding is that these shifts of the Raman active modes of Congo red are probably due to the formation of supramolecular dye aggregates in the presence of water. Therefore, this is not an appropriate diagnostic test for Congo red binding to amyloids.