摘要:

AbstractWe describe a 1 ns molecular dynamics simulation of an 18‐residue peptide (corresponding to a portion pf the H helix of myoglobin) in water. The initial helical conformation progressively frays to a more disordered structure, with the loss of internal secondary structure generally proceeding from the C‐terminus toward the N‐terminus. Although a variety of mechanisms are involved in the breaking of helical hydrogen bonds, the formation of transient turn structures, withi→i+ 3 hydrogen bonds, and bifurcated hydrogen‐bond structures intermediate between α and turn or 310structures is a common motif. In some cases a single water molecule is inserted into an internal hydrogen bond, but it is also common to have several water molecules involved in transient intermediates. Overall, the results provide new information about the detailed mechanisms by which helices are made and broken in aqueou

ISSN:0006-3525    

DOI:10.1002/bip.360311202

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe used time‐dependent fluorescence energy transfer, time–dependent collisional quenching, and global analysis of the data resulting from these through–space and contact interactions to recover the end–to–end distance distributions and diffusion coefficients of flexible fluorescent molecules. The fluorescence decays of covalently linked tryptamine–acceptor and tryptamine–quencher pairs were measured by the frequency–domain method. These data were fit using numerical solutions of the differential equation, which predicts the time–and distance–dependent population of the excited state donors in the presence of energy transfer or collisional quenching, followed by transformation to the frequency domain for nonlinear least–squares comparison with the experimental data. We found that the energy transfer data for the donor–acceptor pair alone were adequate to recover the starting distribution and the end–to–end diffusion coefficient; however, the resolution is dramatically improved by the use of both the through–s

ISSN:0006-3525    

DOI:10.1002/bip.360311203

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

年代:1991

数据来源: WILEY

摘要:

AbstractA chiroptical method of conformational analysis is applied to linear (1 → 3)‐β‐D‐glucans and the dimeric analogues β‐ and α‐laminaribioside. The method is based on a recently developed semiempirical calculational model for saccharide optical activity. We conclude that disaccharide conformational energy maps in the literature represent the effective potential energy surface in aqueous solution well. The positive optical rotation observed with long chains in dilute alkaline solution is not characteristic of any single–chain conformation, and must reflect c

ISSN:0006-3525    

DOI:10.1002/bip.360311204

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

年代:1991

数据来源: WILEY

摘要:

AbstractDynamic laser light scattering studies on the heat aggregation behavior of phycobilisomes (PBS), ferritin, insulin, and immunoglobulin (IgG) in dilute aqueous solutions has been reported. Except for PBS, results are reported for heat aggregation trends in these proteins for three different pH environments (4.0, 7.5, 9.1). For PBS, studies were performed only in the neutral buffer medium (pH 7.5). The experiments were performed in the very dilute concentration regime (between 0.23 and 1.8 gL−1). For all these samples heat aggregation and dissociation trends were found to be linear with temperature. Upon temperature reversal (self‐cooling), hysteresis‐like behavior observed in insulin was found to be predominantly large at pH 7.5. PBS, ferritin, and IgG showed no such behavior at any of three pH values, and retraced their path of aggregation while dissociating on temperature reversal. Heat aggregation and dissociation processes in ferritin were found to be independent of pH. The IgG samples showed smooth aggregation tendency only up to 35°C in the buffer media pH 4.0 and 9.1, whereas for pH 7.0 the same could be observed until 60°C. Low polydispersity in the correlation spectra was observed in case of all these

ISSN:0006-3525    

DOI:10.1002/bip.360311205

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe conformational flexibility of the [Thr6, Leu13ψ(CH2NH) Met14]bombesin (6‐14) nonapeptide has been studied by CD and one‐ and two‐dimensional (1D and 2D) nmr techniques. The CD and nmr parameters in different solvents and in a micellar environment (SDS) are compared with the data collected for the parent bombesin (BN) and [D–Phe12, Leu14]BN. A preliminary investigation on spantide is also reported. In particular, the results obtained from CD measurements indicate that there is a shift from random coil structures, in aqueous solutions, toward folded structures in apolar media (2,2,2‐trifluoroethanol) and in a membrane–mimetic environment (40 mMSDS) for all three peptides, namely BN, [D‐Phe12, Leu14]BN, and [Thr6, Leu13ψ(CH2NH)Met14]BN (6‐14). Spantide, which also possesses some inhibitory activity against BN but very little sequence similarity, even in water, shows an ordered conformation. Nuclear magnetic resonance parameters such as backbone NH‐αCH coupling constant values, amidic temperature coefficients, and the presence of only sequential nuclear Overhauser effects have not provided, so far, any clear evidence for a preferential ordered structure in the peptides studied, and this may be due to rapid exchange among different conformers i

ISSN:0006-3525    

DOI:10.1002/bip.360311206

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe report the complete assignment of the1H‐nmr spectrum of β–casomorphin‐5 in DMSO‐d6solution. With a combination of one‐dimensional, double quantum filtered correlated spectroscopy, homonuclear Hartmann–Hahn, and rotating frame nuclear Overhauser enhancement spectroscopy (ROESY) spectra, we were able to differentiate the four conformers originating from two Xxx‐Pro bonds present in the sequence. Exchange peaks in the ROESY spectra confirmed the presence of four interchanging conformational isomers. Based on integrations, the relative populations of the four species were estimated, while characteristic sequential nuclear Overhauser enhancements (NOEs) were used to determine the orientation of the Xxx‐Pro bonds. This orientation was also shown to correlate with the chemical shift changes for the α protons of both the Xxx and Pro residues. Finally, interresidue NOEs indicate conformational preferences for the aromatic side chains, especially in the a

ISSN:0006-3525    

DOI:10.1002/bip.360311207

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

年代:1991

数据来源: WILEY

摘要:

AbstractStopped flow CD (SFCD) kinetic studies of self–assembly of coiled coils of rabbit αα–tropomyosin and of nonpolymerizable αα–tropomyosin (NPTm) are reported. The protein was denatured in 6Murea buffer, then renatured by 10‐fold dilution into benign saline buffer. Folding was monitored by SFCD in the backbone region (222 nm). Protein chains are shown to be totally unfolded (and separated in the reduced species) in the initial denaturing medium and fully folded as two‐chain coiled coils in the final benign medium. In all cases of folding in benign buffer of totally unfolded chains, two phases were found in the folding process: a fast phase (<0.04 s, the SFCD dead time), in which an intermediate state with about 70% of the equilibrium ellipticity forms; followed by a slower, observable phase that completes the folding. The slow phase is first order (k−1= 1.6 s at 20°C), signifying that chain association for reduced samples occurs in the fast phase. In contrast, folding in benign buffer from an initial state with 70% of the equilibrium ellipticity is all fast, suggesting that the folding intermediate is not an equilibrium species. Cross‐linking at Cys‐190 increases the helix content of the fast‐formed intermediate state to about 85% of the equilibrium value, but leaves the rate constant of the slow phase unchanged. In NPTm, which does not form high aggregates at low ionic strength, the rate of the observable phase is almost independent of ionic strength in the range of ∼ 0.15‐0.6M, but is reduced one to two orders of magnitude by further reduction to 0.026M. In folding from totally unfolded chains, the rate is reduced less than one order of magnitude by changing the final state to about 50% folded. In contrast to folding,unfoldingof αα‐tropomyosin fro

ISSN:0006-3525    

DOI:10.1002/bip.360311208

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

年代:1991

数据来源: WILEY

摘要:

AbstractPhotochemically induced radical reactions involving the lateral sequences and the end macromolecular chain groups of hyaluronic acid in aqueous solutions at 293K were studied by EPR spin trapping technique with DMPO (5,5‐dimethylpyrroline‐1‐oxide). In the first 1‐10 minutes of irradiation EPR indicates spin adducts of two carbon centered radicals with the splitting constants of aN= 1.60 mT, aH= 2.51 mT and aN= 1.56 mT, aH= 2.28 mT. After longer irradiation time (over 10 minutes) dominate two further DMPO adducts of radicals centered on hetero–atoms with splitting constants of aN= 1.44 mT, an = 1.60 mT and of aN= 1‐49 mT, aH= 1.49 mT. Simultaneously, molecular weight followed by SEC decreases, suggesting that UV irradiation leads to the breaking of interglycosidic bonds of hyaluronic acid main macromole

ISSN:0006-3525    

DOI:10.1002/bip.360311209

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

年代:1991

数据来源: WILEY

摘要:

AbstractA tool was developed for enhancement of plasmid penetration into an intact cell, based on increasing DNA hydrophobicity via inclusion into a soluble interpolyelectrolyte complex (IPC) with polycations. The characteristics of formation of DNA IPC with synthetic polycations [poly(N‐ethyl‐4‐vinylpyridinium)bromide (PVP) and PVP modified with 3% of N‐cetyl‐4‐vinylpyridinium units (PVP‐C)] were studied using ultracentrifugation and polyacrylamide gel electrophoresis methods. The conditions were established under which the mixing of DNA and polycation aqueous solutions results in the selfassembly of soluble IPC species. Incorporation of DNA into IPC results in the enhancement of DNA binding with isolatedBacillus subtilismembranes. A considerable increase in the efficiency of transformation ofB. subtiliscells with pBC16 plasmid resulted from incorporation of the plasmid into the IPC wit

ISSN:0006-3525    

DOI:10.1002/bip.360311210

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe hydration shell of several conformations of the polynucleotides poly(dA) · poly(dT), poly (dA) · poly (dU), and poly (dA‐dl) · poly (dT‐dC) has been simulated using the Monte Carlo method (Metropolis sampling). Calculations have shown that the structure of the hydration shell of the minor groove greatly depends on its width. In conformations with a narrowed minor groove, the first layer of the hydration shell of this groove has only one molecule per nucleotide pair that forms H bonds with purine N3 of one pair and pyrimidine O2 of the next pair. The second layer of the hydration shell of such conformations contains molecules that form H bonds between two adjacent molecules of the first layer. The probability of formation of hydration spine is about 20% while the bridges of the first layer are formed with a probability of about 70%.In the first layer of the minor groove of the B–DNA conformation with wide minor groove there are approximately two water molecules per base pair that form H bonds with purine N3 or pyrimidine O2 and with the sugar ring oxygen of the adjacent nucleotide. The probability of simultaneous H bonding of a water molecule with N3 (or O2) and O of sugar ring is about 30%.The results of simulation suggest that hydration spine proposed for the narrowed minor groove of oligonucleotide crystals [H. R. Drew, and R. E. Dickerson (1981)Journal of Molecular Biology, Vol. 151, pp. 535–556] can be formed in fibers of poly (dA) · poly (dT), poly (dA) · poly (dU), and poly (dA‐dl) · poly (dT‐dC) as well as in DNA fragments of these sequences in solution. The role of the hydration shell of the minor groove of DNA double helix in stabilization of certain B‐family conform

ISSN:0006-3525    

DOI:10.1002/bip.360311211

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

年代:1991

数据来源: WILEY