摘要:

AbstractThe molecular structures of four protected isovaline‐ (Iva‐) containing peptides to the pentamer level have been determined by x‐ray diffraction. The peptides aret‐Boc‐Ala‐(S)‐Iva‐Ala‐OMe (t‐Boc :tert‐butyloxycarbonyl; OMe : methoxy) and its (R)‐Iva diastereomer, andt‐Boc‐[Ala‐(R)‐Iva]2‐Ala‐OH and its (S)‐Iva diastereomeric methyl ester analogue. The two tripeptides are folded in an open type II β‐bend conformation. The fully developed right‐handed 310‐helix formed by the (R)‐Iva pentapeptide, which includes an unusual intramolecular (acid) OH ⃛OC(peptide) H bond, is partially unfolded (near the C‐terminus) in the (S) ‐Iva pentapeptide.1H‐nmr and Fourier transform ir absorption studies suggest that in CDCl3solution (a) the two tripeptides maintain a type II β‐bend conformation of comparable stability and (b) both diastereomeric pentapeptide sequences adopt a fully developed 310‐helix. A comparison with the preferred conformation of other extensively investigated Cα,α‐disubstituted glycines is made and the implications for the use of the Iva residue in designing conformationall

ISSN:0006-3525    

DOI:10.1002/bip.360311002

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe accuracy of the Poisson–Boltzmann (PB) approximation and its linearized version is investigated by comparison to results obtained from Monte Carlo simulations. The dependence of the calcium binding constant of the proteincalbindinas a function of salt concentration and mutation is used as a test case. The protein is modeled as a collection of charged and neutral spheres immersed in the electrolyte solution. The PB equation is solved using a finite difference technique on a grid in a spherical polar coordinate system, which is the preferred choice for a globular protein like calbindin. Both MC and PB give quantitative agreement with experimental results. The linearized PB equation is almost as accurate, but it becomes less reliable in systems with divalent ions. However, the linearized PB equation fails to describe the concentration profiles for cations and anions outside the protein even in a 1 : 1 salt solutio

ISSN:0006-3525    

DOI:10.1002/bip.360311003

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe report here a novel approach to label specifically one of the two cryptic, free sulfhydryl groups per subunit of human plasma fibronectin with either an15N,2H‐maleimide spin label or a coumarinylphenyl maleimide fluorescent label. This permits the use of electron spin resonance (ESR) or fluorescence techniques to study molecular dynamics of fibronectin with the label attached to a single site per chain on the protein molecule. The method is based on our observation that upon adsorption of fibronectin to a gelatin‐coated surface, the SH1site, located between the DNA‐binding and the cell‐binding domains, is partially exposed, while the SH2site, located within the carboxyl‐terminal fibrin‐binding domain, remains buried and unreactive. The procedures for the preparation of the selectively labeled fibronectins are described in detail. The physicochemical properties of these single‐site labeled fibronectins, particularly as affected by high salt, heparin, surface binding, and temperature, were characterized by ESR spin‐label and steady‐state fluorescence techniques. The steady‐state fluorescence measurement indicates that both local environments of SH1and SH2sites are relatively hydrophobic, and that the SH2site is more hydrophobic than the SH1site. The ESR results show that heparin or high salt induces an increase in the domainal flexibility in both SH1and SH2regions, perhaps through the disruption of domain–domain interactions in the fibronectin molecule, and that the former is more effective than the latter in producing such an effect. The observed heparin effect is reversible by addition of calcium ions in the SH2regions but not in the SH1regions. In addition, at temperatures above 44°C, both type III homologous regions containing the free sulfhydryl groups are shown to undergo denaturation and aggregation processes. The data presented here suggest that the newly developed method for differential labeling of the free sulfhydryl groups in fibronectin should be useful for mapping the spatial arrangement of structural domains in the protein molecule using spin‐label–spin‐probe and fluorescenc

ISSN:0006-3525    

DOI:10.1002/bip.360311004

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe complex dielectric response of calf thymus DNA in aqueous saline solutions has been measured from 1 MHz to 1 GHz. The results are presented in terms of the relaxation of the incremental contributions to the permittivity and conductivity from the condensed counterions surrounding the DNA molecules. Measurements of the low‐frequency conductivity of the samples also lends support to the condensed counterion interpretatio

ISSN:0006-3525    

DOI:10.1002/bip.360311005

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn the present paper we describe the synthesis, purification, and single crystal x‐ray analysis of the cyclic pentapeptidecyclo‐(L‐Pro‐L‐Pro‐L‐Phe‐β‐Ala‐β‐Ala). The peptide was synthesized by classical solution methods and the cyclization of the free pentapeptide was accomplished in good yields in diluted methylenechloride solution using N,N‐dicyclohexylcarbodiimide. The compound crystallizes in the monoclinic space group P21from hot water with five solvent molecules. The Pro1‐Pro2peptide bond iscisand the molecular conformation is stabilized by an intramolecular hydrogen bond between the CO group of the β‐Ala5and the NH of the Phe3residue. The Pro1‐Pro2segment occupies the relative positions 2 and 3 of a type VIa β‐turn, while theL‐phenylalanyl‐β‐alanyl‐β‐alanine segment is incorporated in a C13‐like ring structure. The crystal packing is characterized by a network of 11 intermolecular hydrogen bonds involving

ISSN:0006-3525    

DOI:10.1002/bip.360311006

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe hinge region links the antigen binding Fabpart to the constant Fcdomain in immunoglobulins. For the hinge peptide derivative [AcThr(OtBu)‐Cys‐Pro‐Pro‐Cys‐Pro‐Ala‐ProNH2]2the assignment of the1H and13C resonances was achieved by two‐dimensional nmr techniques: total correlation spectroscopy (TOCSY), nuclear Ovethauser enhancement spectroscopy (NOESY), rotating frame nuclear Overhauser enhancement spectroscopy (ROESY), heteronuclear multiple quantum coherence (HMQC) transfer, and a HSQC (modified Overbodenhausen experiment) with high resolution in F1, which was several times folded in F1but still phase correctable. Conformational relevant parameters (78 nuclear Overhauser effect distance restraints,3JHHfor prochiral assignments, temperature gradients) were determined by nmr and served as input data for molecular dynamics (MD) structure refinement. A simulated model compound corresponding to the [Cys‐Pro‐Pro‐Cys]2core elongated by the peptide chains in the Faband Fcdirection served as a starting structure for the final MD run. The conformation calculated inin vacuodoes not agree with the C2symmetry required from nmr data, but the structure obtained by a water simulation fulfills the requirement. Here the core of the hinge peptide derivative adopts a polyproline II double helix as in the x‐ray structure of IgG1. Hence, segments responsible for the internal flexibility are located outside the core as confirmed by the flexibility of the so

ISSN:0006-3525    

DOI:10.1002/bip.360311007

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe structure of valinomycin in a range of organic solvents of varying polarity and in detergent and lipid dispersions has been studied by Fourier transform ir Spectroscopy. In solvents of low polarity such as chloroform, ir spectra of valinomycin are fully consistent with the bracelet structure proposed on the basis of nmr Spectroscopy, showing a single narrow amide I component attributable to the presence of β‐turns and a single band arising from nonhydrogen‐bonded ester CO groups. K+complexation results in a downward shift in the amide I band frequency, indicating an increase in the strength of the amide hydrogen bonds, along with a shift to lower frequencies of the ester CO absorption due to a reduction in electron density in these bonds upon complexation. Identical results were obtained with NH 4+, a finding not previously reported.In solvents of both medium (CHCl3/DMSO 3 : 1) and high (pure DMSO) polarity, we find evidence of significant disruption of the internal hydrogen‐bonding network of the peptide and the appearance of a band suggesting the presence of free amide CO groups. In such solvents, complexation with K+and NH 4+was not observed.The structure of valinomycin in detergent micelles resembles that in nonpolar organic solvents. However, changes were found in the amide I and ester carbonyl maxima as2H2O penetrated the micelle which suggest significant interaction between the solvent and peptide. Complexation with K+was reduced in cationic detergent micelles as a result of a decrease in the effective K+concentration due to charge repulsion at the micelle surface.In lipid bilayers the structure again appears identical to that found in chloroform. As in detergent micelles, the amide I and ester carbonyl bands exhibit shifts that indicate interactions with solvent. Complexation with both K+and NH 4+is efficient, producing spectral changes similar to those seen i

ISSN:0006-3525    

DOI:10.1002/bip.360311008

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

年代:1991

数据来源: WILEY

摘要:

AbstractNeurotoxic peptides from venoms of scorpions and honey bees exhibit a consensus pattern in the two disulfide bridgings related to the sequence portions Cys‐X‐Cys and Cys‐X‐X‐X‐Cys. A revised three‐dimensional structure of charybdotoxin, as determined by two‐dimensional nmr spectroscopy, confirms that the consensus cystine dislocation generates in all these toxins a common structural element, i.e., the cystine‐stabilized α‐helical (CSH) motif, which may be correlated with their common ion chann

ISSN:0006-3525    

DOI:10.1002/bip.360311009

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

年代:1991

数据来源: WILEY

摘要:

AbstractStudies of electrophoretic separations of DNA restriction fragments by capillary electrophoresis in solutions of (hydroxyethyl) cellulose (HEC) were performed. Rheological studies were used to confirm that the entanglement threshold (Φ*) for the HEC solutions used is approximately 0.004 g/mL, in good agreement with theoretical predictions. A mesh size an order of magnitude smaller than that found in agarose gels (on a per weight basis) was calculated using polymer‐entanglement theory and was confirmed by electrophoretic measurements. Electrophoretic migration was shown to follow the Ogston regime under most conditions. An approach for obtaining smaller mesh sizes is present

ISSN:0006-3525    

DOI:10.1002/bip.360311010

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe have measured 〈RH〉z, 〈R G2〉 Z½, and 〈M〉wfor individual fractions of the protein α‐crystallin obtained by gel filtration of bovine lens nuclear extracts. A strong and monotonic decrease of 〈RH〉zand 〈M〉wwith increasing elution volume could be observed, indicating a broad size distribution. The experimental results are quantitatively consistent with a polymerization of monomeric units into linear chains, which may have a certain degree of flexibility. Using theoretical expressions for 〈R G2〉 andRHoriginally derived for semiflexible polymers in solution, we can self‐consistently analyse the data from static and dynamic light scattering, and from electron microscopy experiments. We thus obtain detailed information on the molecular weight distribution and the quaternary structure

ISSN:0006-3525    

DOI:10.1002/bip.360311011

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

年代:1991

数据来源: WILEY