Self-assembly of glutamic acid linked paclitaxel dimers into nanoparticles for chemotherapy

In this work, a glutamic acid linked paclitaxel (PTX) dimer (Glu-PTX₂) with high PTX content of 88.9 wt% was designed and synthesized. Glu-PTX₂ could self-assemble into nanoparticles (Glu-PTX₂ NPs) in aqueous solution to increase the water solubility of PTX. Glu-PTX₂ NPs were characterized by electron microscopy and dynamic light scattering, exhibiting spherical morphology and favorable structural stability in aqueous media. Glu-PTX₂ NPs could be internalized by cancer cells as revealed by confocal laser scanning microscopy and exert potent cytotoxicity. It is envisaged that Glu-PTX₂ NPs would be an alternative formulation for PTX, and such amino acid linked drug dimers could also be applied to other therapeutic agents.     

Controllable release of self-assembled reduction-sensitive paclitaxel dimer prodrug and tetrandrine nanoparticles promotes synergistic therapy against multidrug-resistant cancer

BackgroundMultidrug resistance (MDR) is the main reason for chemotherapy failure. Nanocarriers combined delivery of anti-cancer drugs and MDR inhibitors is an effective strategy to avoid MDR and improve the anti-cancer activity of drugs.MethodsTwo paclitaxel (PTX) molecules are linked by disulfide bonds into PTX₂. Then, the PTX₂ and tetrandrine (TET) are coated together by mPEG-PLGA self-assembled NPs for combinational treatment. Microstructure, physiological stability, and cytotoxicity are characterized for the co-loaded NPs.ResultsThe NPs exhibit excellent suitability and blood safety for intravenous injection, specifically responsive to pH 6–7, and promptly initiate chemical degradation. Ex vivo fluorescence microscopy image studies indicate that co-loaded NPs increase drug penetration into cancer cells compared with free drugs. MTT assay demonstrates that co-loaded NPs have higher cytotoxicity against HeLa and the flow cytometric analysis shows that co-loaded NPs trigger more apoptosis than the free drugs. Reactive oxygen species (ROS) assay indicates that the drug-loaded NPs generated higher levels of ROS to accelerate apoptosis in HeLa cells.ConclusionsTET can get desirable effects of inhibiting the MDR in advance by binding with the active site on P-gp, then the disulfide bond of PTX₂ is broken by glutathione (GSH) in cancer cells and decomposed into PTX to inhibit cancer cell proliferation.General significanceOur studies indicate that the co-loaded NPs can potentially overcome the MDR of conventional chemotherapeutic agents.     

Identification of Vaccinia‐H1 Related Phosphatase as an Anticancer Target for 1,2,3,4,6‐O‐Pentagalloylglucose

Protein tyrosine phosphatases are involved in diverse human diseases, including cancer, diabetes and inflammatory disorders. Loss of Vaccinia‐H1 related phosphatase (VHR) has been shown to arrest at the G1‐S and G2‐M transitions of the cell cycle, and to increases cell death of prostate cancer cells through JNK activation, suggesting that VHR can be considered as an anticancer target. In this study, 658 natural products were screened through in vitro enzyme assay to identify VHR inhibitor. Among the VHR‐inhibitory compounds, 1,2,3,4,6‐O‐pentagalloylglucose (PGG) was selected for further study as it has been reported to show antitumor effects against tumor model mice, but its direct target has not been identified. PGG inhibited the catalytic activity of VHR (K_i=53 nm ) in vitro. Furthermore, the incubation of HeLa cervical cancer cells with PGG dramatically decreased cell viability and markedly increased the protein levels of the cleaved PARP, a hallmark of apoptosis. In addition, treatment of HeLa cells with PGG significantly reduced the protein levels of cyclin D1, Bcl‐2 and STAT3 phosphorylation. Taken together, these results suggest that PGG could be a potential therapeutic candidate for the treatment of cervical cancer through VHR inhibition.     

Bundle‐sheath cell regulation of xylem‐mesophyll water transport via aquaporins under drought stress: a target of xylem‐borne ABA?

The hydraulic conductivity of the leaf vascular system (K_leaf) is dynamic and decreases rapidly under drought stress, possibly in response to the stress phytohormone ABA, which increases sharply in the xylem sap (ABA_xyl) during periods of drought. Vascular bundle‐sheath cells (BSCs; a layer of parenchymatous cells tightly enwrapping the entire leaf vasculature) have been hypothesized to control K_leaf via the specific activity of BSC aquaporins (AQPs). We examined this hypothesis and provide evidence for drought‐induced ABA_xyl diminishing BSC osmotic water permeability (P_f) via downregulated activity of their AQPs. ABA fed to the leaf via the xylem (petiole) both decreased K_leaf and led to stomatal closure, replicating the effect of drought. In contrast, smearing ABA on the leaf blade, while also closing stomata, did not decrease K_leaf within 2–3 h of application, demonstrating that K_leaf does not depend entirely on stomatal closure. GFP‐labeled BSCs showed decreased P_f in response to ‘drought’ and ABA treatment, and a reversible decrease with HgCl₂ (an AQP blocker). These P_f responses, absent in mesophyll cells, suggest stress‐regulated AQP activity specific to BSCs, and imply a role for these cells in decreasing K_leaf via a reduction in P_f. Our results support the above hypothesis and highlight the BSCs as hitherto overlooked vasculature sensor compartments, extending throughout the leaf and functioning as ‘stress‐regulated valves’ converting vasculature chemical signals (possibly ABA_xyl) into leaf hydraulic signals.     

Forced-unfolding and force-quench refolding of RNA hairpins

Nanomanipulation of individual RNA molecules, using laser optical tweezers, has made it possible to infer the major features of their energy landscape. Time-dependent mechanical unfolding trajectories, measured at a constant stretching force (f_S) of simple RNA structures (hairpins and three-helix junctions) sandwiched between RNA/DNA hybrid handles show that they unfold in a reversible all-or-none manner. To provide a molecular interpretation of the experiments we use a general coarse-grained off-lattice Gō-like model, in which each nucleotide is represented using three interaction sites. Using the coarse-grained model we have explored forced-unfolding of RNA hairpin as a function of f_S and the loading rate (r_f). The simulations and theoretical analysis have been done both with and without the handles that are explicitly modeled by semiflexible polymer chains. The mechanisms and timescales for denaturation by temperature jump and mechanical unfolding are vastly different. The directed perturbation of the native state by f_S results in a sequential unfolding of the hairpin starting from their ends, whereas thermal denaturation occurs stochastically. From the dependence of the unfolding rates on r_f and f_S we show that the position of the unfolding transition state is not a constant but moves dramatically as either r_f or f_S is changed. The transition-state movements are interpreted by adopting the Hammond postulate for forced-unfolding. Forced-unfolding simulations of RNA, with handles attached to the two ends, show that the value of the unfolding force increases (especially at high pulling speeds) as the length of the handles increases. The pathways for refolding of RNA from stretched initial conformation, upon quenching f_S to the quench force f_Q, are highly heterogeneous. The refolding times, upon force-quench, are at least an order-of-magnitude greater than those obtained by temperature-quench. The long f_Q-dependent refolding times starting from fully stretched states are analyzed using a model that accounts for the microscopic steps in the rate-limiting step, which involves the trans to gauche transitions of the dihedral angles in the GAAA tetraloop. The simulations with explicit molecular model for the handles show that the dynamics of force-quench refolding is strongly dependent on the interplay of their contour length and persistence length and the RNA persistence length. Using the generality of our results, we also make a number of precise experimentally testable predictions.     

STD-NMR studies of two acceptor substrates of GlfT2, a galactofuranosyltransferase from Mycobacterium tuberculosis: Epitope mapping studies

The major structural component of the mycobacterial cell wall, the mycolyl–arabinogalactan–peptidoglycan complex, possesses a galactan core composed of approximately 30 galactofuranosyl (Galf) resides attached via alternating β-(1→6) and β-(1→5) linkages. Recent studies have shown that the entire galactan is synthesized by two bifunctional galactofuranosyltransferases, GlfT1 and GlfT2. We report here saturation transfer difference (STD) NMR studies GlfT2 using two trisaccharide acceptor substrates, β-d-Galf-(1→6)-β-d-Galf-(1→5)-β-d-Galf-O(CH₂)₇CH₃ (2) and β-d-Galf-(1→5)-β-d-Galf-(1→6)-β-d-Galf-O(CH₂)₇CH₃ (3), as well as the donor substrate for the enzyme, UDP-Galf. Epitope mapping demonstrated a greater enhancement toward the ‘reducing’ ends of both trisaccharides, and that UDP-galactofuranose (UDP-Galf) made more intimate contacts through its nucleotide moiety. This observation is consistent with the greater flexibility required within the active site of the reaction between the growing polymer acceptor and the UDP-Galf donor. The addition of UDP-Galf to either 2 or 3 in the presence of GlfT2 generated a tetrasaccharide product, indicating that the enzyme was catalytically active.     

Regulation of non-muscle myosin structure and function

In vertebrate and invertebrate nonmuscle myosins, light- and heavy-chain phosphorylation regulate myosin assembly into filaments, and interaction with actin. Vertebrate non-muscle myosins can exist in vitro in three main states, either ‘folded’ (assembly-blocked) or ‘extended’ (assembly-competent) monomers, and filaments. Light-chain phosphorylation regulates the ‘dynamic equilibrium’ between these states. The ability of the myosin to undergo changes in conformation and state of assembly may be an important mechanism in regulating the organization of the cytoskeleton and cell motility.     

Fe2+ binding on amyloid β‐peptide promotes aggregation

The metal ions Zn²⁺, Cu²⁺, and Fe²⁺ play a significant role in the aggregation mechanism of Aβ peptides. However, the nature of binding between metal and peptide has remained elusive; the detailed information on this from the experimental study is very difficult. Density functional theory (dft) (M06‐2X/6‐311++G (2df,2pd) +LANL2DZ) has employed to determine the force field resulting due to metal and histidine interaction. We performed 200 ns molecular dynamics (MD) simulation on Aβ_1‐42‐Zn²⁺, Aβ_1‐42‐Cu²⁺, and Aβ_1‐42‐Fe²⁺ systems in explicit water with different combination of coordinating residues including the three Histidine residues in the N‐terminal. The present investigation, the Aβ_1‐42‐Zn²⁺ system possess three turn conformations separated by coil structure. Zn²⁺ binding caused the loss of the helical structure of N‐terminal residues which transformed into the S‐shaped conformation. Zn²⁺ has reduced the coil and increases the turn content of the peptide compared with experimental study. On the other hand, the Cu²⁺ binds with peptide, β sheet formation is observed at the N‐terminal residues of the peptide. Fe²⁺ binding is to promote the formation of Glu22‐Lys28 salt‐bridge which stabilized the turn conformation in the Phe19‐Gly25 residues, subsequently β sheets were observed at His13‐Lys18 and Gly29‐Gly37 residues. The turn conformation facilitates the β sheets are arranged in parallel by enhancing the hydrophobic contact between Gly25 and Met35, Lys16 and Met35, Leu17 and Leu34, Val18 and Leu34 residues. The Fe²⁺ binding reduced the helix structure and increases the β sheet content in the peptide, which suggested, Fe²⁺ promotes the oligomerization by enhancing the peptide‐peptide interaction. Proteins 2016; 84:1257–1274. © 2016 Wiley Periodicals, Inc.     

Diffusion limitations and metabolic factors associated with inhibition and recovery of photosynthesis from drought stress in a C3 perennial grass species

Stomatal closure and metabolic impairment under drought stress limits photosynthesis. The objective of this study was to determine major stomatal and metabolic factors involved in photosynthetic responses to drought and recovery upon re‐watering in a C₃ perennial grass species, Kentucky bluegrass (Poa pratensis L.). Two genotypes differing in drought resistance, ‘Midnight’ (tolerant) and ‘Brilliant’ (sensitive), were subjected to drought stress for 15 days and then re‐watered for 10 days in growth chambers. Single‐leaf net photosynthetic rate (A), stomatal conductance (g_s) and transpiration rate (Tr) decreased during drought, with a less rapid decline in ‘Midnight’ than in ‘Brilliant’. Photochemical efficiency, Rubisco activity and activation state declined during drought, but were significantly higher in ‘Midnight’ than in ‘Brilliant’. The relationship between A and internal leaf CO₂ concentration (A/Ci curve) during drought and re‐watering was analyzed to estimate the relative influence of stomatal and non‐stomatal components on photosynthesis. Stomatal limitation (Ls %), non‐stomatal limitation (Lns %), CO₂ compensation point (CP) and dark respiration (Rd) increased with stress duration in both genotypes, but to a lesser extent in ‘Midnight’. Maximum CO₂ assimilation rate (A_max), carboxylation efficiency (CE) and mesophyll conductance (g_m) declined, but ‘Midnight’ had significantly higher levels of A_max, CE and g_m than ‘Brilliant’. Maximum carboxylation rate of Rubisco (V_cmax) and ribulose‐1,5‐bisphospate (RuBP) regeneration capacity mediated by maximum electron transport rate (J_max) decreased from moderate to severe drought stress in both genotypes, but to a greater extent in ‘Brilliant’ than in ‘Midnight’. After re‐watering, RWC restored to about 90% of the control levels in both genotypes, whereas A, g_s, Tr and Fv/Fm was only partially recovered, with a higher recovery level in ‘Midnight’ than in ‘Brilliant’. Rubisco activity and activation state restored to the control level after re‐watering, with more rapid increase in ‘Midnight’ than in ‘Brilliant’. The values of Ls, Lns, CP and Rd declined, and A_max, CE, V_cmax, J_max and g_m increased after re‐watering, with more rapid change in all parameters in ‘Midnight’ than in ‘Brilliant’. These results indicated that the maintenance of higher A and A_max under drought stress in drought‐tolerant Kentucky bluegrass could be attributed to higher Rubico activation state, higher CE and less stomatal limitation. The ability to resume metabolic activity (A_max, CE, Fv/Fm and Rubisco) was observed in the drought‐tolerant genotype and is the most likely cause for the increased recuperative ability of photosynthesis. Incomplete recovery of photosynthesis upon re‐watering could be attributable to lasting stomatal limitations caused by severe drought damage in both genotypes. Promoting rapid stomatal recovery from drought stress may be critical for plants to resume full photosynthetic capacity in C₃ perennial grass species.     

The Chinese family as instituted fantasy: or,rescuing kinship imaginaries from the ‘symbolic’

This article revisits well‐travelled ethnographic portrayals of traditional Chinese family dynamics to draw attention to desire as a product of family life and to how crucial elements of family organization and ideology can be understood, in turn, as effects of desire – that is, as instituted fantasies. Although my case in point is the Chinese family, the analysis addresses the category ‘family’ cross‐culturally. In any of its variations, the ‘family’ exists at two synergistically implicated levels: first, it comprises an important part of the reality into which individuals are socialized; second, it embodies in instituted form individuals' attempts to realize – to bring into being – social arrangements as they would like them to be. In the Chinese case, at least two ironies are embedded in this synergy. First, women are primary producers and reproducers of the family in the ‘real world’, despite the fact that patriliny as ‘instituted fantasy’ downplays or veils their agency. Second, the normative subordination of the son to a patriarchal father, expressed and mediated through institutions including ancestor worship and valorization of filial piety, veils a valorizing of the son as agent or protagonist of filial action. Although ultimately unrealizable, patrilineal and familial fantasies animate Chinese family life and are thus an important constituent of Chinese realities. To these ends the analysis re‐purposes ‘the symbolic’ and ‘imaginaries’, categories widely employed in contemporary gender studies and social theory, arguing that understanding kinship enjoins incorporating desire's role both in defining institutions and in motivating their creators.     

Defining CO2 and O2 syndromes of marine biomes in the Anthropocene

Research efforts have intensified to foresee the prospects for marine biomes under climate change and anthropogenic drivers over varying temporal and spatial scales. Parallel with these efforts is the utilization of terminology, such as ‘ocean acidification’ (OA) and ‘ocean deoxygenation’ (OD), that can foster rapid comprehension of complex processes driving carbon dioxide (CO₂) and oxygen (O₂) concentrations in the global ocean and thus, are now widely used in discussions within and beyond academia. However, common usage of the terms ‘acidification’ and ‘deoxygenation’ alone are subjective and, without adequate contextualization, have the potential to mislead inferences over drivers that may ultimately shape the future state of marine ecosystems. Here we clarify the usage of the terms OA and OD as global, climate change‐driven processes and discuss the various attributes of elevated CO₂ and reduced O₂ syndromes common to coastal ecosystems. We support the use of the existing terms ‘coastal acidification’ and ‘coastal deoxygenation’ because they help differentiate the sometimes rapid and extreme nature of CO₂ and O₂ syndromes in coastal ecosystems from the global, climate change‐driven processes of OA and OD. Given the complexity and breadth of the processes involved in altering CO₂ and O₂ concentrations across marine ecosystems, we provide a workflow to enable contextualization and clarification of the usage of existing terms and highlight the close link between these two gases across spatial and temporal scales in the ocean. These distinctions are crucial to guide effective communication of research within the scientific community and guide policymakers responsible for intervening on the drivers to secure desirable future ocean states.     

DEVELOPMENT OF A ‘BIPOLAR’ R‐INDEX1

A new ‘bipolar’ R‐index analysis was proposed and evaluated. Eighteen judges evaluated red color in eight wine samples by comparing each sample with the control. Judges indicated whether the sample had ‘more’, the 'same’, or ‘less’ red color than the control, and whether they were sure or unsure of their decision. Three computational methods were used to examine the results: the ‘traditional’ R‐index, the ‘bipolar’ R‐index (R_more or R_less) and the ‘weighted‐bipolar’ R‐index. While all three methods provided consistent results, the ‘bipolar’ R‐indices reflected bidirectional differences among the samples thus providing more information. A refinement to the computation (‘weighted‐bipolar’ R‐index) was an approach for eliminating the bias associated with overestimation of the sample size and accordingly changed some of the significance levels. Further research is currently underway to expand the scope and application of this method.     

Genetic trends of conformation traits and genetic correlations to osteochondrosis in boars

The objective of our study was to investigate the heritabilities and genetic correlations between traits from a linear exterior assessment system and osteochondrosis (OC) measured by computed tomography (CT), and in addition, to study the genetic trend in a population where the conformation traits have been included in the breeding goal. The data material consisted of phenotypes from a total of 4571 Norsvin Landrace test boars. At the end of the test period, all boars were subjected to a detailed exterior assessment system. Within 10 days of the assessment, the boars were CT scanned for measuring OC. The total score of osteochondrosis (OCT), used in this study, is the sum of phenotypes from the assessment on the medial and lateral condyles at the distal end of both the humerus and the femur of the right and the left leg of the boar based on images from CT. The exterior assessment traits included in the study were; ‘front leg knee’ (FKNE), ‘front leg pasterns’ (FPAS), ‘front leg stance’ (FSTA), ‘front leg twisted pasterns’ (FFLK), ‘hind leg stance’, ‘hind leg pasterns’ (HPAS), ‘hind leg standing under’ (HSTU), ‘hind leg small inner toe’, ‘dipped back’, ‘arched back’ (ARCH) and ‘waddling hindquarters’ (WADL). The estimation of (co)variance components and breeding values were performed using bivariate animal genetic models. Breeding values for HSTU, HPAS, FPAS, WADL and OCT traits were additional outputs from the same bivariate analyses. The lowest heritability was found for FFLK (h²_FFLK=0.05), whereas FPAS was estimated to have the highest heritability (h²_FPAS=0.36), and OCT demonstrating a heritability of 0.29. Significant genetic correlations were found between several traits; the strongest correlation was between FSTA and FFLK (0.94), which was followed by the correlation between FPAS and FKNE (0.69). The traits ARCH and FSTA had significant genetic correlations to OCT, whereas all other genetic correlations between OCT and the conformation traits were low and not significantly different from 0. Our study shows positive genetic trends for the conformation traits included in the breeding goal. In general, low genetic correlations between conformation traits and OC were observed in our study.     

A molecular dynamics study of the 41-56 beta-hairpin from B1 domain of protein G.

The structural and dynamical behavior of the 41-56 beta-hairpin from the protein G B1 domain (GB1) has been studied at different temperatures using molecular dynamics (MD) simulations in an aqueous environment. The purpose of these simulations is to establish the stability of this hairpin in view of its possible role as a nucleation site for protein folding. The conformation of the peptide in the crystallographic structure of the protein GB1 (native conformation) was lost in all simulations. The new equilibrium conformations are stable for several nanoseconds at 300K (>10 ns), 350 K (>6.5 ns), and even at 450 K (up to 2.5 ns). The new structures have very similar hairpin-like conformations with properties in agreement with available experimental nuclear Overhauser effect (NOE) data. The stability of the structure in the hydrophobic core region during the simulations is consistent with the experimental data and provides further evidence for the role played by hydrophobic interactions in hairpin structures. Essential dynamics analysis shows that the dynamics of the peptide at different temperatures spans basically the same essential subspace. The main equilibrium motions in this subspace involve large fluctuations of the residues in the turn and ends regions. Of the six interchain hydrogen bonds, the inner four remain stable during the simulations. The space spanned by the first two eigenvectors, as sampled at 450 K, includes almost all of the 47 different hairpin structures found in the database. Finally, analysis of the hydration of the 300 K average conformations shows that the hydration sites observed in the native conformation are still well hydrated in the equilibrium MD ensemble.     

Models for the 3(10)-helix/coil,pi-helix/coil,and alpha-helix/3(10)-helix/coil transitions in isolated peptides.

Models for the 3(10)-helix/coil and pi-helix/coil equilibria have been derived. The theory is based on classifying residues into helical or nonhelical (coil) conformations. Statistical weights are assigned to residues in a helical conformation with an associated helical hydrogen bond, a helical conformation with no hydrogen bond, an N-cap position, a C-cap position, or the reference coil conformation. The models for alpha-helix formation and 3(10)-helix formation have also been combined to describe a three-state equilibrium in which alpha-helical, 3(10)-helical, and coil conformations are populated. The results are compared with the modified Lifson-Roig theory for the alpha-helix/coil equilibrium. The comparison accounts for the experimental observations that 3(10)-helices tend to be short and pi-helices are not favored for any length. This work may provide a framework for quantitatively rationalizing experimental work on isolated 3(10)-helices and mixed 3(10)-/alpha-helices.     

A single‐stranded conformational polymorphism (SSCP)‐derived quantitative variable to monitor the virulence of a Barley yellow dwarf virus‐PAV (BYDV‐PAV) isolate during adaptation to the TC14 resistant wheat line

A standardized single‐stranded conformational polymorphism (SSCP) procedure is proposed as an alternative to the time‐consuming biological characterization of Barley yellow dwarf virus‐PAV (BYDV‐PAV) isolates. Using this procedure, six of 21 overlapping regions used to scan the viral genome gave patterns specific to ‘4E’ (avirulent) or ‘4T’ (‘4E’‐derived virulent) isolates. The calibration of samples and integration of SSCP patterns corresponding to the nucleotide region 1482–2023 allowed the estimation of P_T values that reflect the proportions of a ‘4T’‐specific band. Analysis of the biological (area under the pathogen progress curve) and molecular (P_T) data suggested a positive linear relation between these variables. Moreover, sequence analysis of the nucleotide region 1482–2023 highlighted the presence of a nucleotide polymorphism (C/A₁₈₃₅) which can be considered as a candidate for virus–host interactions linked to the monitored virulence. According to these parameters, P_T values associated with ‘4E’‐ and ‘4T’‐derived populations show that: (i) long‐term infection of a BYDV‐PAV isolate on the ‘TC14’ resistant host leads to the fixation of virulent individuals in viral populations; and (ii) the introduction of susceptible hosts in successive ‘TC14’ infections results in the maintenance of low virulence of the populations. Thus, the presented study demonstrates that SSCP is a useful tool for monitoring viral populations during the host adaptation process. The described impact of host alternation provides new opportunities for the use of the ‘TC14’ resistance source in BYDV‐resistant breeding programmes. This study is part of the global effort made by the scientific community to propose sustainable alternatives to the chemical control of this viral disease.     

A peptide study of the relationship between the collagen triple-helix and amyloid

Type XXV collagen, or collagen‐like amyloidogenic component, is a component of amyloid plaques, and recent studies suggest this collagen affects amyloid fibril elongation and has a genetic association with Alzheimer's disease. The relationship between the collagen triple helix and amyloid fibrils was investigated by studying peptide models, including a very stable triple helical peptide (Pro‐Hyp‐Gly)₁₀, an amyloidogenic peptide GNNQQNY, and a hybrid peptide where the GNNQQNY sequence was incorporated between (GPO)_n domains. Circular dichroism and nuclear magnetic resonance (NMR) spectroscopy showed the GNNQQNY peptide formed a random coil structure, whereas the hybrid peptide contained a central disordered GNNQQNY region transitioning to triple‐helical ends. Light scattering confirmed the GNNQQNY peptide had a high propensity to form amyloid fibrils, whereas amyloidogenesis was delayed in the hybrid peptide. NMR data suggested the triple‐helix constraints on the GNNQQNY sequence within the hybrid peptide may disfavor the conformational change necessary for aggregation. Independent addition of a triple‐helical peptide to the GNNQQNY peptide under aggregating conditions delayed nucleation and amyloid fibril growth. The inhibition of amyloid nucleation depended on the Gly‐Xaa‐Yaa sequence and required the triple‐helix conformation. The inhibitory effect of the collagen triple‐helix on an amyloidogenic sequence, when in the same molecule or when added separately, suggests Type XXV collagen, and possibly other collagens, may play a role in regulating amyloid fibril formation. © 2012 Wiley Periodicals, Inc. Biopolymers 97: 795–806, 2012.     

Sequential polypeptides containing arginine as histone models: synthesis and conformational studies

The sequential polypeptides (L -Arg-X-Gly)_n, where X represents amino acid residues Ala, Val, and Leu, were prepared as models of arginine-rich histones to be used in studying their structure and their interactions with DNA. The polymerization was carried out on the pentachlorophenyl active esters of the appropriate tripeptides, while the toluene-4-sulfonyl group was used for protecting the arginine guanido group. CD was employed to investigate the conformation of (L -Arg-X-Gly)_n polymers in aqueous solutions, at different pH, as well as in trifluoroenthanol and hexafluoroisopropyl alcohol solutions. In aqueous solutions (at pH 7 and 12) the prepared sequential polymers behaved as a random coil. The CD spectra in various trifluoroethanol–water or hexafluoroisopropyl alcohol–water mixtures indicated that the degree of helical conformation of the studied polytripeptides increased in the order of Ala → Val → Leu. The opposite was true for the β-structure. Characteristics of β-turn are excluded from the poly(L -Arg-L -Leu-Gly), which assumed the most pronounced helical conformation. The poly(L -Arg-L -Val-Gly) exerts a significant preference to the β-turn structure compared to that of poly(L -Arg-L -Ala-Gly). Thus the probability for helical, β-structure or β-turn conformations of the polymers was analyzed in relation to the bulkiness and length, and to the special features of the X-residue side chain (β-branching). We concluded that the prepared sequential arginine-containing polypeptides are plausible models for histone fractions, f₃ and f₂α₁.