摘要:

AbstractAggregation of filipin in aqueous medium and filipin‐induced changes in cholesterol micelles have been studied using intensity and dynamic light scattering. The dependencies of filipin aggregate dimensions on concentration, solvent, and temperature were studied, and revealed that the aggregates do not have a well‐defined geometry, i.e., a critical micelle concentration cannot be detected and stable structures are not formed. The aggregates are of sizeRg≈ 110 nm andRh≈ 63 nm, referring to the radius of gyration and hydrodynamic radius, respectively. In the concentration range studied (1 μM

ISSN:0006-3525    

DOI:10.1002/bip.360340402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

Abstract1H‐NMR and molecular dynamics simulations in vacuo and in water of (1 → 4)‐α‐D‐galacturono‐disaccharide were performed. The results of the molecular dynamics simulations showed that the molecule fluctuates between two conformations characterized by different values of torsion angles around the glycosidic linkage and two different intramolecular hydrogen bonds. When these conformations are extrapolated to a regular polymeric structure, they generate pectic acid compatible with a 21‐ or a right‐handed 31‐helix. © 1994 J

ISSN:0006-3525    

DOI:10.1002/bip.360340403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance and optical experiments are combined to determine the rms amplitude of local angular motion of purines in DNA in solution. A 12 base‐pair duplex DNA with the sequence d (CGCGAATTCGCG)2is deuterated at the H8 positions of adenine and guanine by exchange with solvent dklstwxzat 55°C. The deuterium nmr spectrum of this DNA is measured at 30 mg/mL at 30°C in an 11.76 Tesla magnet (76.75 MHz). The time‐resolved fluorescence polarization anisotropies (FPA) of thissamesample and also a greatly diluted sample (0.215 mg/mL) were measured after addition of ethidium. FPA measurements of the dilute sample yield the hydrodynamic radius,RH= 9.94 ± 0.2 Å, while those at the nmr concentration are employed to characterize the collective motions in terms of either an enhanced viscosity or dimer formation. The rms amplitude of local angular motion was determined by analyzing the2H‐nmr spectrum, in particular the line width, using recently developed theory for the transverse relaxation rate (R 2Q) together with essential information about the collective motions from these and other optical studies. When the principal‐axis frame of the electric field gradient tensor is assumed to undergo overdamped libration around each of its three body‐fixed axes in an isotropic deflection potential, then the rms amplitude of local angular motion around any single axis is found to lie in the range 10°–11°, provided the high DNA concentration acts to enhance the viscosity, and is about 9°–11°, if it acts to produce end‐to‐end dimers. The proton nmr relaxation data of Eimer et al. are reanalyzed and shown to yield an rms amplitude of angular motion of the cytosme H5–H6 internuclear vector of 9°–10°, depending upon its orientation with respect to the helix axis. In all of these analyses, full account is taken of the collective twisting and bending deformations, which have a small but significant effect on the results. It is shown that the rms amplitudes of local angular motion do not depend strongly on the model (potential), provided that isotropic rotation around the same number of axes is allowed and that one compares rms angles of the same dimensionality. The rms amplitudes of local angular motion in solution are comparable to those observed for the same sequence at low levels of hydration in the solid s

ISSN:0006-3525    

DOI:10.1002/bip.360340404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe formation of α‐helical assembly by complexing biologically active peptides with de novo designed protein is described. The de novo designed protein described here is a cystinelinked 4‐helix bundle protein constructed with 80 amino acid residues and forms a hydrophobic core region surrounded by 4 helices in an aqueous solution. The biologically active peptides, such as melittin and human growth hormone releasing factor, contain the sequences that are able to form amphiphilic helices. These peptides alone do not form the α‐helix structure in a diluted solution with low ion strength. But on mixing with the designed helix bundle protein, the peptides are strongly bound to the protein with the induction of α‐helical structure in the biologically active peptides. The content of induced α‐helix is in accord with that estimated from the amphiphilic sequence. The results mean that a novel architecture composed of α‐helices is formed. Fluorescent and temperature‐scanning measurement revealed that the α‐helical assembly is constructed with hydrophobic interaction. Also, it is shown by means of fluorescence depolarization that the assembly has a compact globular form corresponding to 1 : 1 complex. © 199

ISSN:0006-3525    

DOI:10.1002/bip.360340405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPolypeptide α‐carbon backbones were modeled as freely rotating chains made up of spherical monomers. The monomers were assigned an abstract binary “hydrophobicity” property that could be either present or absent. Under the assumption that “hydrophobic” residues tend to cluster together, away from the polar solvent, three‐dimensional conformations of random copolymers of “hydrophobic” and “hydrophilic” monomers were calculated by a novel algorithm based on distance geometry techniques. The simulated molecules were globular and compact, in shape, and possessed distinct hydrophobic cores, indicating that our method was capable of reproducing some of the important global features of real polypeptides. © 1994

ISSN:0006-3525    

DOI:10.1002/bip.360340406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe protein folding behavior of a polyelectrolyte protein, bovine dentine phosphophoryn (BDPP), in the pH range of 1.82–11.0 has been investigated. One‐ and two‐dimensional nmr spectroscopy has been utilized to obtain proton spin assignments for amino acid residues in D2O and in H2O. One‐dimensional31P‐nmr experiments verify the existence of three separate classes ofO‐phosphoserine (PSer) resonances in BDPP (α, β, χ), representing three distinct PSer residue populations at pH 6.94. By means of pH titration and1H‐nmr, five populations of Asp residues can be identified. Three of these populations exhibit secondary inflection points on their pH titration curves that correspond to an observed pKaof 6.17–6.95. The presence or absence of secondary inflection points for Asp populations and the31P‐nmr chemical shift dispersion for the three PSer residue populations indicate that BDPP may be comprised of homologous (Asp‐Asp)n. (PSer‐PSer)n, and heterologous (PSer‐Asp)nsequences arranged into polyelectrolyte cluster regions.The pH titration also revealed that certain populations of Ser, Gly, and Pro residues in BDPP exhibit pH‐dependent resonance frequency shifts. The “apparent” pK, for the transition points of these frequency shifts corresponds to either the pK a1of Pser monophosphatc ester and/or the pKaof Asp COOH group of BDPP polyelectrolyte regions. On the basis of these transition points, we can assign four types of Ser, Gly, or Pro‐containing “intervening” regions in BDPP, based on their sensitivity to protonation and deprotonation events occurring at (Asp)n, (PSer)n, or (PSer‐Asp)nanionic cluster regions that flank the intervening regions.Our1H‐ninr experiments also reveal that BDPP assumes a folded conformation at low pH. As the pH increases, this conformation undergoes several unfolding transitions as the BDPP molecule assumes more open conformations in response to increased electrostatic repulsion between polyelectrolyte anionic regions in the protein. These folding‐unfolding transitions are mediated by the intervening regions, which act as “hinges” to allow the polyelectrolyte regions to fold re

ISSN:0006-3525    

DOI:10.1002/bip.360340407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractMonte Carlo simulated annealing is applied to the tertiary structure prediction of a 17‐residue synthetic peptide, which is known by experiment to exhibit high helical content at low pH. Two dielectric models are considered: sigmoidal distance‐dependent dielectric function and a constant dielectric function (ϵ = 2). Starting from completely random initial conformations, our simulations for both dielectric models at low pH gave many helical conformations. The obtained low‐energy conformations are compared with the nuclear Overhauser effect spectroscopy cross‐peak data for both main chain and side chains, and it is shown that the results for the sigmoidal dielectric function are in remarkable agreement with the experimental data. The results predict the existence of two disjoint helices around residues 5–9 and 11–16, while nmr experiments imply significant α‐helix content between residues 5 and 14. Simulations with high pH, on the other hand, hardly gave a helical conformation, which is also in accord with the experiment. These findings indicate that when side chains are charged, electrostatic interactions due to these charges play a major role in the helix stability. Our results are compared with the previous 500 ps molecular dynamics simulations of the same peptide. It is argued that simulated annealing is superior to molecular dynamics in two respects: (1) direct folding of α‐helix from completely random initial conformations is possible for the former, whereas only unfolding of an α‐helix can be studied by the latter; (2) while both methods predict high helix content for low pH, the results for high pH agree with experiment (low helix content) only for the former method. © 199

ISSN:0006-3525    

DOI:10.1002/bip.360340408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWe have determined the partial molar volumes, expansibilities, and adiabatic compressibilities of glycine, diglycine, triglycine, tetraglycine, and pentaglycine over the temperature range 18–55°C. These data were analyzed and interpreted in terms of the hydration of these short oligoglycines and their constituent groups. From our results, we have estimated the contributions of the peptide group to the partial molar volume and the partial molar adiabatic compressibility of these oligoglycines. Based on these data, we propose that each of the polar atomic groups of the peptide bond forms approximately two hydrogen bonds with adjacent water molecules. Furthermore, the temperature dependence of the partial molar volume suggests that water that solvates the polar groups of a peptide linkage behaves more like a “normal” liquid than does bulk water, which exhibits its well‐known anomalous liquid properties. © 1994 John Wiley&

ISSN:0006-3525    

DOI:10.1002/bip.360340409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360340410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360340411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY