Defined sequence segments of the small heat shock proteins HSP25 and alphaB-crystallin inhibit actin polymerization.

The interaction of small heat shock proteins (sHSPs) with the actin cytoskeleton has been described and some members of this family, e.g. chicken and murine HSP25 (HSP27), inhibit the polymerization of actin in vitro. To analyse the molecular basis of this interaction, we synthesized a set of overlapping peptides covering the complete sequence of murine HSP25 and tested the effect of these peptides on actin polymerization in vitro by fluorescence spectroscopy and electron microscopy. Two peptides comprising the sequences W43 to R57 (peptide 6) and I92 to N106 (peptide 11) of HSP25 were found to be potent inhibitors of actin polymerization. Phosphorylation of N-terminally extended peptide 11 at serine residues known to be phosphorylated in vivo resulted in decline of their inhibitory activity. Interestingly, peptides derived from the homologous peptide 11 sequence of murine alphaB-crystallin showed the same behaviour. The results suggest that both HSP25 and alphaB-crystallin have the potential to inhibit actin polymerization and that this activity is regulated by phosphorylation.     

Effect of low-molecular peptides on the transformation of fibrinogen into fibrin

The influence of synthetic peptides on fibrinogen transformation to fibrin under the action of thrombin and fibrin-monomer polymerization was investigated. Peptides Gly-Pro-Arg-Pro; Gly-Pro-Arg-Pro-Lys; Gly-Pro-Arg-Pro-Lys-Boc; Gly-Pro-Arg-Pro-Arg are specific inhibitors of fibrin formation. These peptides interfere with the hydrolysing effect of thrombin due to binding to the central domain of fibrinogen. The interaction of peptides with peripheral D-domains of fibrin-monomer may account for polymerization inhibition. The latter peptide has the largest anticoagulation activity. It is likely that arginine in the fifth position stabilizes the structure of the peptides, with the additional epsilon NH2-group activating its interaction with protein.     

Catalysis by human leukocyte elastase. Aminolysis of acyl-enzymes by amino acid amides and peptides

Acyl-enzymes of human leukocyte elastase (HLE) were generated in situ during the hydrolysis of peptide thiobenzyl esters and served as substrates for aminolysis by a variety of amino acid amides and short peptide nucleophiles. For amino acid amides, there is a positive correlation between nucleophilic reactivity toward N-methoxysuccinyl (MeOSuc)-Ala-Ala-Pro-Val-HLE and the hydrophobicity of the side chain. For peptides, nucleophilicity toward MeOSuc-Ala-Ala-Pro-Val-HLE decreases dramatically with increasing chain length. Combined, these results suggest that substrate specificity for the P1' residue may be more dependent on side chain hydrophobicity than on specific, structural features of the side chain and there may be no important binding interactions available past S1'. Kinetic parameters were also determined for the nucleophilic reactions of PheNH2 and TyrNH2 with MeOSuc-Pro-Val-HLE, MeOSuc-Ala-Pro-Val-HLE, MeOSuc-Ala-Ala-Pro-Val-HLE, and MeOSuc-Ala-Ala-Pro-Ala-HLE. Reactivity of these acyl-enzymes toward nucleophilic attack displays no dependence on peptide chain length but does increase significantly for the substrate with Ala at P1. This same correlation between reactivity and acyl-enzyme structure is also seen for nucleophilic attack by water.     

Synthesis and study of biological activity of stereoisomeric dipeptides containing tyrosine and arginine residues

Series of methyl esters of stereoisomeric dipeptides of the sequences Tyr-Arg and Arg-Tyr has been synthesized by classic methods of the peptide chemistry. The study of their reactivity towards thrombin and trypsin has shown that the kinetic parameters of enzyme-catalyzed hydrolyses of stereoisomeric compounds differ in values essentially. Testing the synthetic peptides on analgic effect, on inhibition of the reaction fibrinogen with thrombin or on influence upon the process of fibrin-monomer polymerization has shown that these biological effects depend on peptide structure and on configuration of amino acid residues forming the peptides.     

MARCKS-Related Protein Binds to Actin without Significantly Affecting Actin Polymerization or Network Structure

Actinis a 42-kDa protein which, due to its ability to polymerize into filaments (F-actin), is one of the major constituents of the cytoskeleton. It has been proposed that MARCKS (an acronym for myristoylated alanine-rich C kinase substrate) proteins play an important role in regulating the structure and mechanical properties of the actin cytoskeleton by cross-linking actin filaments. We have recently reported that peptides corresponding to the effector domain of MARCKS proteins promote actin polymerization and cause massive bundling of actin filaments. We now investigate the effect of MARCKS-related protein, a 20-kDa member of the MARCKS family, on both filament structure and the kinetics of actin polymerization in vitro. Our experiments document that MRP binds to F-actin with micromolar affinity and that the myristoyl chain at the N-terminus of MRP is not required for this interaction. In marked contrast to the effector peptide, binding of MRP is not accompanied by an acceleration of actin polymerization kinetics, and we also could not reliably observe an actin cross-linking activity of MRP.     

MARCKS-related protein binds to actin without significantly affecting actin polymerization or network structure. Myristoylated alanine-rich C kinase substrate

Actinis a 42-kDa protein which, due to its ability to polymerize into filaments (F-actin), is one of the major constituents of the cytoskeleton. It has been proposed that MARCKS (an acronym for myristoylated alanine-rich C kinase substrate) proteins play an important role in regulating the structure and mechanical properties of the actin cytoskeleton by cross-linking actin filaments. We have recently reported that peptides corresponding to the effector domain of MARCKS proteins promote actin polymerization and cause massive bundling of actin filaments. We now investigate the effect of MARCKS-related protein, a 20-kDa member of the MARCKS family, on both filament structure and the kinetics of actin polymerization in vitro. Our experiments document that MRP binds to F-actin with micromolar affinity and that the myristoyl chain at the N-terminus of MRP is not required for this interaction. In marked contrast to the effector peptide, binding of MRP is not accompanied by an acceleration of actin polymerization kinetics, and we also could not reliably observe an actin cross-linking activity of MRP.     

Dissolved Divalent Metal and pH Effects on Amino Acid Polymerization: A Thermodynamic Evaluation

Polymerization of amino acids is a fundamentally important step for the chemical evolution of life. Nevertheless, its response to changing environmental conditions has not yet been well understood because of the lack of reliable quantitative information. For thermodynamics, detailed prediction over diverse combinations of temperature and pH has been made only for a few amino acid–peptide systems. This study used recently reported thermodynamic dataset for the polymerization of the simplest amino acid “glycine (Gly)” to its short peptides (di-glycine and tri-glycine) to examine chemical and structural characteristics of amino acids and peptides that control the temperature and pH dependence of polymerization. Results showed that the dependency is strongly controlled by the intramolecular distance between the amino and carboxyl groups in an amino acid structure, although the side-chain group role is minor. The polymerization behavior of Gly reported earlier in the literature is therefore expected to be a typical feature for those of α-amino acids. Equilibrium calculations were conducted to examine effects of dissolved metals as a function of pH on the monomer–polymer equilibria of Gly. Results showed that metals shift the equilibria toward the monomer side, particularly at neutral and alkaline pH. Metals that form weak interaction with Gly (e.g., Mg²⁺) have no noticeable influence on the polymerization, although strong interaction engenders significant decrease of the equilibrium concentrations of Gly peptides. Considering chemical and structural characteristics of Gly and Gly peptides that control their interactions with metals, it can be expected that similar responses to the addition of metals are applicable in the polymerization of neutral α-amino acids. Neutral and alkaline aqueous environments with dissolved metals having high affinity with neutral α-amino acids (e.g., Cu²⁺) are therefore not beneficial places for peptide bond formation on the primitive Earth.     

Importance of the release of strand 1C to the polymerization mechanism of inhibitory serpins.

Serpin polymerization is the underlying cause of several diseases, including thromboembolism, emphysema, liver cirrhosis, and angioedema. Understanding the structure of the polymers and the mechanism of polymerization is necessary to support rational design of therapeutic agents. Here we show that polymerization of antithrombin is sensitive to the addition of synthetic peptides that interact with the structure. A 12-m34 peptide (homologous to P14-P3 of antithrombin reactive loop), representing the entire length of s4A, prevented polymerization totally. A 6-mer peptide (homologous to P14-P9 of antithrombin) not only allowed polymerization to occur, but induced it. This effect could be blocked by the addition of a 5-mer peptide with s1C sequence of antithrombin or by an unrelated peptide representing residues 26-31 of cholecystokinin. The s1C or cholecystokinin peptide alone was unable to form a complex with native antithrombin. Moreover, an active antitrypsin double mutant, Pro 361-->Cys, Ser 283-->Cys, was engineered for the purpose of forming a disulfide bond between s1C and s2C to prevent movement of s1C. This mutant was resistant to polymerization if the disulfide bridge was intact, but, under reducing conditions, it regained the potential to polymerize. We have also modeled long-chain serpin polymers with acceptable stereochemistry using two previously proposed loop-A-sheet and loop-C-sheet polymerization mechanisms and have shown both to be sterically feasible, as are "mixed" linear polymers. We therefore conclude that the release of strand 1C must be an element of the mechanism of serpin polymerization.     

Trimetaphosphate Activates Prebiotic Peptide Synthesis across a Wide Range of Temperature and pH

The biochemical activation of amino acids by adenosine triphosphate (ATP) drives the synthesis of proteins that are essential for all life. On the early Earth, before the emergence of cellular life, the chemical condensation of amino acids to form prebiotic peptides or proteins may have been activated by inorganic polyphosphates, such as tri metaphosphate (TP). Plausible volcanic and other potential sources of TP are known, and TP readily activates amino acids for peptide synthesis. But de novo peptide synthesis also depends on pH, temperature, and processes of solvent drying, which together define a varied range of potential activating conditions. Although we cannot replay the tape of life on Earth, we can examine how activator, temperature, acidity and other conditions may have collectively shaped its prebiotic evolution. Here, reactions of two simple amino acids, glycine and alanine, were tested, with or without TP, over a wide range of temperature (0–100 °C) and acidity (pH 1–12), while open to the atmosphere. After 24 h, products were analyzed by HPLC and mass spectrometry. In the absence of TP, glycine and alanine readily formed peptides under harsh near-boiling temperatures, extremes of pH, and within dry solid residues. In the presence of TP, however, peptides arose over a much wider range of conditions, including ambient temperature, neutral pH, and in water. These results show how polyphosphates such as TP may have enabled the transition of peptide synthesis from harsh to mild early Earth environments, setting the stage for the emergence of more complex prebiotic chemistries.     

Synthesis, characterization, and evaluation of PS-PPDC resin: a novel flexible cross-linked polymeric support for solid-phase organic synthesis

The present study describes the synthesis of different mole densities of poly(propylene glycol)dimethacrylate cross-linked resins using monomer units such as styrene and 4-chloromethyl styrene and its evaluation as an ideal support toward different stages of solid-phase peptide synthesis. Free radical generated aqueous suspension polymerization has been followed for polymerization and the formation of resin was characterized using infrared and carbon-13 spectroscopic techniques. Surface morphology of resin was examined by scanning electron microscopy. The polymerization reaction was investigated with respect to the effect of amount of cross-linking agent to verify the swelling, loading, and the mechanical stability of resin. Solvent imbibition abilities in commonly used solvents were measured and compared to commercially available Merrifield as well as reported styrene-acryloyloxyhydroxypropyl methacrylate-tripropyleneglycol diacrylate (SAT resins. The chemical inertness of the support was also checked with different reagents used for solid-phase peptide synthesis. The suitability of support was demonstrated by synthesizing biologically potent Endothelin class of linear peptides by Fmoc strategy and compared to SAT resin. The purities of synthetic peptides were analyzed by high-performance liquid chromatography and corresponding masses by matrix-assisted laser desorption/ionisation-time of flight analysis.     

Atomic force microscopy reveals defects within mica supported lipid bilayers induced by the amyloidogenic human amylin peptide

To date, over 20 peptides or proteins have been identified that can form amyloid fibrils in the body and are thought to cause disease. The mechanism by which amyloid peptides cause the cytotoxicity observed and disease is not understood. However, one of the major hypotheses is that amyloid peptides cause membrane perturbation. Hence, we have studied the interaction between lipid bilayers and the 37 amino acid residue polypeptide amylin, which is the primary constituent of the pancreatic amyloid associated with type 2 diabetes. Using a dye release assay we confirmed that the amyloidogenic human amylin peptide causes membrane disruption; however, time-lapse atomic force microscopy revealed that this did not occur by the formation of defined pores. On the contrary, the peptide induced the formation of small defects spreading over the lipid surface. We also found that rat amylin, which has 84% identity with human amylin but cannot form amyloid fibrils, could also induce similar lesions to supported lipid bilayers. The effect, however, for rat amylin but not human amylin, was inhibited under high ionic conditions. These data provide an alternative theory to pore formation, and how amyloid peptides may cause membrane disruption and possibly cytotoxicity.     

A new direction for anticoagulants: Inhibiting fibrin assembly with PEGylated fibrin knob mimics

Current anticoagulants target coagulation factors upstream from fibrin assembly and polymerization (i.e., formation of fibrin clot). While effective, this approach requires constant patient monitoring since pharmacokinetics and pharmacodynamics vary from patient to patient. To address these limitations, we developed an alternative anticoagulant that effectively inhibits fibrin polymerization. Specifically, we investigated PEGylated fibrin knob “A” peptides, evaluating the effect of both polyethylene glycol (PEG) chain length (0, 2, 5, and 10–30 kDa) and knob peptide sequence (GPRPAAC, GPRPFPAC, and GPRPPERC) on inhibiting fibrin polymerization (i.e., clot formation). Thrombin‐initiated clotting assays with purified fibrinogen were performed to compare clot formation with each peptide–PEG conjugate. Results indicated a biphasic effect of PEG chain length, whereby, active‐PEG conjugates demonstrated increasingly enhanced inhibition of fibrin polymerization from 0 to 5 kDa PEG. However, the anticoagulant activity diminished to control levels for PEG chains above 5 kDa. Ultimately, we observed a 10‐fold enhancement of anticoagulant activity with active peptides PEGylated with 5 kDa PEG compared to non‐PEGylated knob peptides. The sequence of the active peptide significantly influenced the anticoagulant properties only at the highest 1:100 molar ratio where GPRPFPAC‐5 kDa PEG and GPRPPERC‐5 kDa PEG demonstrated significantly lower percent clottable protein than GPRPAAC‐5 kDa PEG. Moreover, human plasma treated with the active 5 kDa PEG conjugate exhibited delayed prothrombin time to within the therapeutic range specified for oral anticoagulants. Collectively, this study demonstrated the utility of PEGylated fibrin knob peptides as potential anticoagulant therapeutics. Biotechnol. Bioeng. 2011;108: 2424–2433. © 2011 Wiley Periodicals, Inc.     

Polymerization site in the beta chain of fibrin: mapping of the B beta 1-55 sequence

The formation of a fibrin clot occurs through binding of putative complementary sites, called fibrin polymerization sites, located in the NH2- and COOH-terminal domains of fibrin monomer molecules. In this study, we have investigated the structure of the NH2-terminal fibrin polymerization site by using fibrinogen-derived peptides and fragments. Fibrinogen was digested with Crotalus atrox protease III, to two major molecular species: a Mr 325,000 derivative (Fg325) and a peptide of Mr 5000. The peptide and its thrombin-cleavage product were purified by ion-exchange and reverse-phase HPLC; the authenticity of the B beta 1-42 and beta 15-42 peptides, respectively, was confirmed by amino acid sequencing. Since Fg325 had decreased thrombin coagulability, we addressed the question of whether the peptide B beta 1-42 contained a fibrin polymerization site. In order to identify and map the site, the peptides B beta 1-42 and beta 15-42 were tested for their ability to inhibit fibrin monomer polymerization. In addition the following peptides prepared by chemical synthesis were also tested: beta 15-18, beta 15-26, beta 24-42, beta 40-54, beta 50-55, and alpha 17-19-Pro. While B beta 1-42 had no inhibitory activity, the peptide devoid of fibrinopeptide B, beta 15-42, was a strong inhibitor. The peptides beta 15-18, beta 15-26, and beta 15-42 decreased the rate of fibrin polymerization by 50% at a molar excess of the peptide to fibrin monomer of 500, 430, and 50, respectively. The peptides beta 24-42, beta 40-54, and beta 50-55 were inactive.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of hemoglobin S polymerization in vitro by a novel 15-mer EF-helix beta73 histidine-containing peptide

Our mutational studies on Hb S showed that the Hb S beta73His variant (beta6Val and beta73His) promoted polymerization, while Hb S beta73Leu (beta6Val and beta73Leu) inhibited polymerization. On the basis of these results, we speculated that EF-helix peptides containing beta73His interact with beta4Thr in Hb S and compete with Hb S, resulting in inhibition of Hb S polymerization. We, therefore, studied inhibitory effects of 15-, 11-, 7-, and 3-mer EF-helix peptides containing beta73His on Hb S polymerization. The delay time prior to Hb S polymerization increased only in the presence of the 15-mer His peptide; the higher the amount, the longer the delay time. DIC image analysis also showed that the fiber elongation rate for Hb S polymers decreased with increasing concentration of the 15-mer His peptide. In contrast, the same 15-mer peptide containing beta73Leu instead of His and peptides shorter than 11 amino acids containing beta73His including His alone showed little effect on the kinetics of polymerization and elongation of polymers. Analysis by protein-chip arrays showed that only the 15-mer beta73His peptide interacted with Hb S. CD spectra of the 15-mer beta73His peptide did not show a specific helical structure; however, computer docking analysis suggested a lower energy for interaction of Hb S with the 15-mer beta73His peptide compared to peptides containing other amino acids at this position. These results suggest that the 15-mer beta73His peptide interacts with Hb S via the beta4Thr in the betaS-globin chain in Hb S. This interaction may influence hydrogen bond interaction between beta73Asp and beta4Thr in Hb S polymers and interfere in hydrophobic interactions of beta6Val, leading to inhibition of Hb S polymerization.     

The specific NH2-terminal sequence Ac-EEED of alpha-smooth muscle actin plays a role in polymerization in vitro and in vivo

The blocking effect of the NH2-terminal decapeptide of alpha-smooth muscle (SM) actin AcEEED-STALVC on the binding of the specific monoclonal antibody anti-alpha SM-1 (Skalli, O., P. Ropraz, A. Trzeviak, G. Benzonana, D. Gillessen, and G. Gabbiani. 1986. J. Cell Biol. 103:2787-2796) was compared with that of synthetic peptides modified by changing the acetyl group or by substituting an amino acid in positions 1 to 5. Using immunofluorescence and immunoblotting techniques, anti-alpha SM-1 binding was abolished by the native peptide and by peptides with a substitution in position 5, indicating that AcEEED is the epitope for anti-alpha SM-1. Incubation of anti-alpha SM- 1 (or of its Fab fragment) with arterial SM actin increased polymerization in physiological salt conditions; the antibody binding did not hinder the incorporation of the actin antibody complex into the filaments. This action was not exerted on skeletal muscle actin. After microinjection of the alpha-SM actin NH2-terminal decapeptide or of the epitopic peptide into cultured aortic smooth muscle cells, double immunofluorescence for alpha-SM actin and total actin showed a selective disappearance of alpha-SM actin staining, detectable at approximately 30 min. When a control peptide (e.g. alpha-skeletal [SK] actin NH2-terminal peptide) was microinjected, this was not seen. This effect is compatible with the possibility that the epitopic peptide traps a protein involved in alpha-SM actin polymerization during the dynamic filament turnover in stress fibers. Whatever the mechanism, this is the first evidence that the NH2 terminus of an actin isoform plays a role in the regulation of polymerization in vitro and in vivo.     

Natriuretic peptides cause relaxation of human esophageal mucosal muscle

Natriuretic peptides have been demonstrated to cause relaxation of the human gallbladder muscle through interaction with natriuretic peptide receptor-B (NPR-B/NPR2). Effects of natriuretic peptides in the human esophageal muscle were unknown. To investigate the effects of natriuretic peptides in the human esophagus, we measured relaxation of muscularis mucosae strips isolated from the human esophagus caused by C-type natriuretic peptide (CNP), brain natriuretic peptide (BNP), atrial natriuretic peptide (ANP) and des[Gln(18), Ser(19), Gly(20), Leu(21), Gly(22)]ANP(4-23) amide (cANP(4-23)), a selective natriuretic peptide receptor-C (NPR-C) agonist. In endothelin-1 or carbachol-contracted mucosal muscle strips, CNP caused moderate, sustained and concentration-dependent relaxation. BNP caused a very mild relaxation whereas ANP and cANP(4-23) did not cause any relaxation. CNP was much more potent than BNP and ANP in causing relaxation. These suggest the existence of NPR-B mediating relaxation. The CNP-induced relaxation was not affected by tetrodotoxin or atropine in endothelin-1-contracted esophageal strips and not by tetrodotoxin in carbachol-contracted strips, indicating a direct effect of CNP on the human esophageal muscularis mucosae. Taken together, these results demonstrate that natriuretic peptides cause relaxation of the muscularis mucosae of the human esophagus and suggest that the relaxation is through interaction with NPR-B. Natriuretic peptides may play an important role in the control of human esophageal motility.     

Modified-peptide inhibitors of amyloid beta-peptide polymerization.

Cellular toxicity resulting from nucleation-dependent polymerization of amyloid beta-peptide (Abeta) is considered to be a major and possibly the primary component of Alzheimer's disease (AD). Inhibition of Abeta polymerization has thus been identified as a target for the development of therapeutic agents for the treatment of AD. The intrinsic affinity of Abeta for itself suggested that Abeta-specific interactions could be adapted to the development of compounds that would bind to Abeta and prevent it from polymerizing. Abeta-derived peptides of fifteen residues were found to be inhibitory of Abeta polymerization. The activity of these peptides was subsequently enhanced through modification of their amino termini with specific organic reagents. Additional series of compounds prepared to probe structural requirements for activity allowed reduction of the size of the inhibitors and optimization of the Abeta-derived peptide portion to afford a lead compound, cholyl-Leu-Val-Phe-Phe-Ala-OH (PPI-368), with potent polymerization inhibitory activity but limited biochemical stability. The corresponding all-D-amino acyl analogue peptide acid (PPI-433) and amide (PPI-457) retained inhibitory activity and were both stable in monkey cerebrospinal fluid for 24 h.     

Natriuretic peptides cause relaxation of human and guinea-pig gallbladder muscle through interaction with natriuretic peptide receptor-B

Atrial natriuretic peptide (ANP) binding sites have been demonstrated in the guinea-pig gallbladder muscle with unclear function. To investigate effects of natriuretic peptides in the gallbladder, we measured relaxation of isolated human and guinea-pig gallbladder strips caused by natriuretic peptides, including C-type natriuretic peptide (CNP), brain natriuretic peptide (BNP) and ANP, as well as des[Gln18, Ser19, Gly20, Leu21, Gly22]ANP(4-23) amide (cANP(4-23)), a selective natriuretic peptide receptor-C (NPR-C) agonist. Results in the human gallbladder were similar to those in the guinea-pig gallbladder. CNP, BNP, ANP and cANP(4-23) alone did not cause contraction or relaxation in resting gallbladder strips. However, in carbachol or endothelin-1-contracted strips, CNP caused moderate, sustained and concentration-dependent relaxation. The relaxation was not affected by tetrodotoxin or atropine in endothelin-1-contracted gallbladder strips and not by tetrodotoxin in carbachol-contracted strips. These indicate a direct effect of CNP on the gallbladder muscle. The relative potencies for natriuretic peptides to cause relaxation were CNP>BNP> or = ANP. cANP(4-23) did not cause relaxation. These indicate the existence of the natriuretic peptide receptor-B (NPR-B) mediating the relaxation. Taken together, these results demonstrate that natriuretic peptides cause relaxation of human and guinea-pig gallbladder muscle through interaction with the natriuretic peptide receptor-B.     

Characterization of the actin polymerization-inhibiting protein from chicken gizzard smooth muscle

An actin polymerization-inhibiting protein, occurring in crude preparations of vinculin from chicken gizzard, has been found to be heterogeneous. The molecular masses of the polymerization-inhibiting peptides have been reported to range from 20 kDa to 80 kDa [Schr?er, E. & Wegner, A (1985) Eur. J. Biochem. 153, 515-520]. In this paper, a 21-kDa peptide was isolated from the bulk of the other peptides by gel chromatography. The 21-kDa peptide was identified as a polymerization-inhibiting peptide by its ability to retard nucleated actin polymerization and to bind polymeric actin when it was blotted onto nitrocellulose. Antiserum raised to the 21-kDa peptide was found to react with almost all peptides of the blotted heterogeneous polymerization-inhibiting protein. The same peptides which reacted with antiserum cosedimented with polymeric actin. The major peptides of the blotted polymerization-inhibiting protein bound polymeric actin. The largest peptide which reacted with antiserum and cosedimented with polymeric actin had a molecular mass of 85 kDa. The results suggest that the preparation of polymerization-inhibiting protein contains mainly polymerization-inhibiting peptides and only some contaminants, and that all the polymerization-inhibiting peptides are proteolytic fragments stemming from a common precursor.     

Effect of the aminoacid composition of model α-helical peptides on the physical properties of lipid bilayers and peptide conformation: a molecular dynamics simulation

The interaction of a model Lys flanked α-helical peptides K₂-X₂₄-K₂, (X = A,I,L,L+A,V) with lipid bilayers composed of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) both, in a gel and in a liquid-crystalline state, has been studied by molecular dynamics simulations. It has been shown that these peptides cause disordering of the lipid bilayer in the gel state but only small changes have been monitored in a liquid-crystalline state. The peptides affect ordering of the surrounding lipids depending on the helix stability which is determined by amino acid side chains – their volume, shape, etc. We have shown that the helix does not keep the linear shape in all simulations but often bends or breaks. During some simulations with a very small difference between hydrophobic length of peptide and membrane thickness the peptide exhibits negligible tilt. At the same time changes in peptide conformations during simulations resulted in appearance of superhelix.