摘要:

AbstractThermodynamics of unfolding of lysozyme cross‐linked between Glu 35 and Trp 108 were studied in solutions of various concentrations of 1‐propanol (1‐PrOH) at pH 3.7 by means of scanning microcalorimetry. The transition temperature for the cross‐linked lysozyme increases by 17–19°C due to cross‐linking at every concentration of 1‐PrOH. This corresponds to the increase in the unfolding Gibbs free energy of about 28 kJ · mol−1, which is independent of the concentration of 1‐PrOH. It was found that the unfolding enthalpy of cross‐linked lysozyme is only slightly larger than that of intact one, and the unfolding entropy of the cross‐linked one is nearly equal to that of the intact one, if both are compared at the same temperature. The stabilization mechanism for the cross‐linked lysozyme is discussed on the basis o

ISSN:0006-3525    

DOI:10.1002/bip.360280602

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe velocity and orientation of T4 and λ DNA have been measured for the first 20 s during pulsed‐field gel electrophoresis in order to clarify the DNA motions that occur. For a square pulse with field strengthE= 10 V/cm, the velocity of λ DNA increases gradually to 10.5 μm/s in 1.0 s, declines to 8.6 μm/s, and then rises to a plateau value of 9.3 μm/s after 4 s. T4 DNA behaves similarly, but more slowly. Parallel measurements of fluorescence‐detected linear dichroism show that the DNA becomes substantially aligned with its chain axis parallel to the electrophoretic fieldEafter the pulse is applied. The alignment also shows an overshoot, an undershoot, and a plateau comparable to those seen for velocity. When the field strength increases, both the velocity and the alignment reach their peaks more quickly. For all field strengths and both molecular weights, the velocity peak occurs when the molecular center of mass has moved 0.3 to 0.5L, whereLis the chain contour length. A qualitative model is

ISSN:0006-3525    

DOI:10.1002/bip.360280603

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

年代:1989

数据来源: WILEY

摘要:

AbstractIn the context of dynamic Monte Carlo simulations on a model protein confined to a tetrahedral lattice, the interplay of protein size and tertiary structure, and the requirements for an all‐or‐none transition to a unique native state, are investigated. Small model proteins having a primary sequence consisting of a central bend neutral region flanked by two tails having an alternating hydrophobic/hydrophilic pattern of residues are seen to undergo a continuous transition to a β‐hairpin collapsed state. On increasing the length of the tails, the β‐hairpin structural motif is found to be in equilibrium with a four‐member β‐barrel. Further increase of the tail length results in the shift of the structural equilibrium to the four‐member β‐barrel. The random coil to β‐barrel transition is of an all‐or‐none character, but while the central turn is always the desired native bend, the location of the turns involving the two external strands is variable. That is, β‐barrels having the external stands that are two residues out of register are also observed in the transition region. Introduction into the primary sequence of two additional regions that are at the very least neutral toward turn formation produces an all‐or‐none transition to the unique, native, four‐member β‐barrel. Various factors that can augment the stability of the native conformation are explored. Overall, these folding simulations strongly indicate that the general rules of globular protein folding are rather robust—namely, one requires a general pattern of hydrophobic/hydrophilic residues that allow the protein to have a welldefined interior and exterior and the presence of regions in the amino acid sequence that at the very least are locally indifferent to turn formation. Since no site‐specific interactions between hydrophobic and hydrophilic residues are required to produce a unique four‐member β‐barrel, these simulations strongly suggest that site sp

ISSN:0006-3525    

DOI:10.1002/bip.360280604

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe nature of the equilibrium conformational transition from the denatured state to a four‐member α‐helical bundle was studied employing a dynamic Monte Carlo algorithm in which the model protein chain was confined to a tetrahedral lattice. The model chain was allowed to hunt over all phase space, the target native state was not assumed a priori, and no site‐specific interactions were introduced. The exterior vs the interior part of the protein is distinguished by the pattern of hydrophilic and hydrophobic interactions encoded into the primary sequence. The importance of a statistical preference for forming bends, as a function of bend location in the primary sequence, and helical wheel type cooperative interactions were examined, and the necessary conditions for collapse of the chain to the unique native structure were investigated. It was found that an amphipathic pattern of hydrophobic/hydrophilic interactions along with a statistical preference of the central residues for bend formation are sufficient to obtain the four‐helix bundle. The transition to the native state has an all‐or‐no

ISSN:0006-3525    

DOI:10.1002/bip.360280605

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe complete assignment of resonances in the proton nmr spectrum of the 1–34 amino acid fragment of human parathyroid hormone [hPTH(1–34)], determined using a combination of one‐ and two‐dimensional nmr techniques at 500 MHz, is described. In particular, homonuclear Hartmann–Hahn experiments, recorded in H2O and D2O, are used to resolve ambiguities in the connectivities between the highly overlapped resonances in the aliphatic region of the spectrum. One‐dimensional multiple quantum filtering experiments are used to identify serine and phenylalanine spin systems. Analyses of the through‐bond and through‐space connectivities in the αH‐NH fingerprint regions of the correlated spectroscopy (COSY) and nuclear Overhauser effect spectroscopy (NOESY) spectra lead to the assignment of resonances to specific amino acid residues in the polypeptide. Examination of the observed NOE cross peaks indicates that hPTH(1–34) has no detectable secondary structural elements

ISSN:0006-3525    

DOI:10.1002/bip.360280606

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

年代:1989

数据来源: WILEY

摘要:

AbstractSequence‐specific photomodification of oligodeoxynucleotide pAGAGTATTGACTTA (“a target”) has been carried out with the aid of complementary fluorescent probes. Such a probe consisted of oligodeoxynucleotide pAATACTCT and a chromophore group attached to its 5′ end. Three different derivatives of ethidium bromide were used as a chromophore. The photomodification was induced by nitrogen laser radiation (337 nm, 15 MW /cm2). The irradiation induces the following photodamages: target cleavage at the specific binding site with a cutting off of the 8‐mer from its 5′ end (yield up to 12%), formation of specific covalent adduct target‐probe with a yield of 20–70%, and piperidine‐sensitive target modifications with a 7–27% yield (for different chromophores). The total yield of specific photodamages of all kinds is 50–80%. The target cleavage and generation of piperidine‐sensitive modifications are optically nonlinear processes. Piperidine treatment of the irradiated samples led to specific cleavage of the target with the yield up to 40%. All kinds of observed modifications are not influenced by high concentrations of free radical scavengers: 1.3MtBuOH and 10 mMcystamine. The pattern of cleavage indicates that the most probable position of the chromophore is between T8 and G9 of the target, i.e., the chromophore stacks on top of the last A · T base pair of the duplex. The aggregate of evidence is in agreement with the mechanism of nonlinear photomodification (the cleavage and generation of piperidine‐sensitive modifications) based on the transfer of two‐photon excitation energy from t

ISSN:0006-3525    

DOI:10.1002/bip.360280607

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

年代:1989

数据来源: WILEY

摘要:

AbstractTwo‐dimensional nmr data on a bulge‐containing oligodeoxyribonucleotide,5′dGATGGGCAG · dCTGACCCATC, and a regular oligomer of similar sequence,5′dGATGGCAG · dCTGCCATC, are presented. The nonexchangeable protons are assigned from sequential nuclear Overhauser effect spectroscopy (NOESY) connectivities. The two‐dimensional NOE (NOESY) and correlated (COSY) spectra of the bulge‐containing oligomer are compared to those of the perfect 8‐mer. Experimental proton‐proton distances are determined from NOESY spectra acquired with mixing times of 100, 150, and 200 ms, using comparable distances in the B‐DNA region of the molecule as a calibration. With this approach, measured distances do not depend systematically on mixing time. Energy minimization techniques are used to calculate a three‐dimensional structure for the bulge‐containing oligomer in agreement with the nmr data. The helix is of the B family, with the extra adenine stacked into the helix, and the he

ISSN:0006-3525    

DOI:10.1002/bip.360280608

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe physiological importance of heparin is due to its strong interaction with bivalent counterions, especially Ca2+. A diffusional approach of this property is presented in this article: the observable is the self‐diffusion coefficient of the counterions, as a function of the ratio of the polyelectrolyte over the added salt concentrations. All the results are in agreement with a simple “quasi‐chemical model” in which two different states are assumed for the counterions: “free” or “bound.” The proportions of these two types of ions are calculated according to the distribution function of the counterions around the polyion. We assume that those of counterions located at a distance closer thana, the characteristic distance, are bound; the others are free. The ionic distribution function is evaluated by a numerical integration of a cell model Poisson–Boltzmann equation. Finally, this model leads to a very good agreement with the experimental results, if the radius of heparin polyion is assumed

ISSN:0006-3525    

DOI:10.1002/bip.360280609

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

年代:1989

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360280601

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

年代:1989

数据来源: WILEY