摘要:

AbstractInteractions between the α‐helix peptide dipoles and charged groups close to the ends of the helix were found to be an important determinant of α‐helix stability in a previous study.1The charge on the N‐terminal residue of the C‐peptide from ribonuclease A was varied chiefly by changing the α‐NH2blocking group, and the correlation of helix stability with N‐terminal charge was demonstrated. An alternative explanation for some of those results is that the succinyl and acetyl blocking groups stabilize the helix by hydrogen bonding to an unsatisfied main‐chain NH group. The helix dipole model is tested here with peptides that contain either a free α‐NH 3+α‐COO−groups, and no other charged groups that would titrate with similar pKa's. This model predicts that α‐NH3α‐COO‐ groups are helix‐destabilizingand that the destabilizing interactions are electrostatic in origin. The hydrogen bonding model predicts that α‐NH3and α‐COO‐ groups are not themselves helix‐destabilizing, but that an acetyl or amide blocking group at the N‐ or C‐ terminus, respectively, stabilizes the helix by hydrogen bonding to an unsatisfied main‐chain NH or CO group.The results are as follows: (1) Removal of the charge from α‐NH3and α‐COO‐ groups by pH titration stabilizes an α‐helix. (2) The increase in helix stability on pH titration of these groups is close to the increase produced by adding an acetyl or amide blocking group. (3) The helix‐stabilizing effect of removing the charge from α‐NH3and α‐COO‐ groups by pH titration is screened by increasing the NaCl concentration, and therefore the effect is electrostatic in origin. (4) Replacing the C‐terminal amide blocking group with a methylester blocking group, w

ISSN:0887-3585    

DOI:10.1002/prot.340050102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of the folded conformation of a protein on the rate of deamidation of a specific asparaginyl residue has been determine. Native and unfolded ribonuclease A (RNase A) could be compared under identical conditions, because stable unfolded protein was generated by breaking irreversibly the protein disulfide bonds.Deamidation of the labile Asn‐67 residue of RNase A was followedelectrophoretically and chromatographically. At 80°C, similar rates of deamidation were observed for the disulfidebonded form, which is thermally unfolded, and the reduced form. At 37°C and pH 8, however, the rate of deamidation of native RNase A was negligible, and was more than 30‐fold slower than that of reduced, unfolded RNase A. This demonstrates that the Asn‐67 residue is located in a local conformation in the native protein that greatly inhibits deamidation. This conformation is the β‐turn of resi

ISSN:0887-3585    

DOI:10.1002/prot.340050103

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe construction of a template‐assembled synthetic protein (TASP) designed to contain both a 4‐helix bundle and a β‐barrel as two folding “domains” is described. For thede novodesign of proteins, amphiphilic helices (α) and β‐sheets (β) are covalently attached to a template peptide (T) carrying functional side chains suitably oriented to promote intarmolecular folding of the secondary structure blocks into a characteristic packing arrangement, i.e., T8‐(4α)(4β). The design of this new macromolecule was assisted by computer modeling, which suggested a low‐energy conformation with tight hydrophobic packing of the secondary structure subunits. Solid‐phase synthesis of the “two‐domain” TASP molecule was achieved using orthogonal protection techniques. The solution properties as well as circular dichroism (CD) and infrared spectroscopy (IR) data under various experimental conditions are consistent with the folded confo

ISSN:0887-3585    

DOI:10.1002/prot.340050104

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe Subtilisin family of proteases has four members of known sequence and structure: subtilisin Carlsberg, Subtilisin novo, proteinase K, and thermitase. Using thermitase as a test case, we ask two questions. How good are methods for model building a three‐dimensional structure of a protein based on sequence homology to a known structure? And what are the molecular causes of thermostability? First, we compare predicted models of thermitase, refined by energy minimization and varied by molecular dynamics, with the preliminary crystal structure. The predictions work best in the conserve structural core and less well in seven loop regions involving insertions and deletions relative to Subtilisin. Here, variation of loop regions by molecular dynamics simulationin vacuofollowed by energy minimization does not improve the prediction since we find no correlation betweenin vacuoenergy and correctness of structure when comparing local energy minima. Second, in order to identify the molecular case of thermostability we confront hypotheses erived by calculation of the details of interatomic interactions with inactivation experiments. As a result, we can exclude salt bridges and hydrophobic interactions as main cause of thermostability. Based on a combination of theoretical and experimental evidence, the unusually tight binding of calcium by thermitase emerges as the most likely single influence responsible for its increased thermostabilit

ISSN:0887-3585    

DOI:10.1002/prot.340050105

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

年代:1989

数据来源: WILEY

摘要:

AbstractThermal unfolding experiments on bacteriorhodopsin in mixed Phospholipid/detergent micelles were performed. Bacteriorhodopsin was extracted from the purple membrane in a denatured state and then renatured in the micellar system. The purpose of this study was to compare the changes, if any, in the structure and stability of a membrane protein that has folded in a nonnative environment with results obtained on the native system, i.e., the purple membrane. The purple membrane crystalline lattice is an added factor that may influence the structural stability of bacteriorhodopsin. Micelles containing bacteriorhodopsin are uniformly sized disks 105 ± 13 Å in diameter (by electron microscopy) and have an estimated molecular mass of 210 kDa (by gel filtration HPLC). The near‐UV CD spectra (which is indicative of tertiary structure) for micellar bacteriorhodopsin and the purple membrane are very similar. In the visible CD region of retinal absorption, the double band seen in the spectrum of the purple membrane is replaced with a broad positive band for micellar bacteriorhodopsin, indicating that in micelles, bacteriorhodopsin is monomeric. The plot of denaturational temperature vs. pH for micellar bacteriorhodopsin is displaced downward on the temperature axis, illustrating the lower thermal stability of micellar bacteriorhodopsin when compared to the purple membrane at the same pH. Even though micellar bacteriorhodopsin is less stable, similar changes in response to pH and temperature are seen in the visible absorption spectra of micellar bacteriorhodopsin and the purple membrane. This demonstrates that changes in the protonation state or temperature have a similar affect on the local environment of the chromophore and the protein conformation. We conclude that the tertiary structure of the bacteriorhodopsin monomer is essentially the same in micelles and the purple membrane. On the other hand, in the synthetic mixed micelle system, the packing between the nonnative amphiphiles and bacteriorhodopsin is probably not optimal, protein‐protein interactions have been lost, and thehelical packing may be looser because the crystalline lattice is absent. Itis likely that a combination of these effects leads to the decreased stability of micellar bacteriorhod

ISSN:0887-3585    

DOI:10.1002/prot.340050106

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe active conformation of an icenucleation protein, whose major portion consists of a long polypeptide segment of nearly repetitive octapeptides, is predicted by the analyses of conformational energy and the mechanism of crystal growth. The protein ideally has an exact octapeptide repetition and is assumed to have a helical conformation. The present study searched for low‐energy helical conformations and each of the obtained low‐energy conformations examined as to whether it has a surface structure that can promote crystal formation. Two conformations obtained were good candidates for an ice nucleus. Both were found to have on their surfaces an arrangement of hydrogen‐bonding sites, which fits well with those of hydrogen bonds in hexagonal ice crystal. Further, one of the two conformations had a hexagonal conformational symmetry consistent with the hexagonal ice crystal structure. The other conformation had apentagonal conformational symmetry that could enable the growth of an ice crystal–dendritic polycrystalline snow crystal–which grows on metastable

ISSN:0887-3585    

DOI:10.1002/prot.340050107

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

年代:1989

数据来源: WILEY

摘要:

AbstractAlthough ionizable groups are known to play important roles in the assembly, catalytic, and regulatory mechanisms ofEscherichia coliaspartate transcarbamylase, these groups have not been characterized in detail. We report the application of static accessibility modified Tanford‐Kirkwood theory to model electrostatic effects associated with the assembly of pair of chains, subunits, and the holoenzyme. All of the interchain interfaces except R1–R6 are stabilized by electrostatic interactions by −2 to −4 kcal−m−1at pH 8. The pH dependence of the electrostatic component of the free energy of stabilization ofintrasubunitcontacts (C1–C2 and R1–R6) is qualitatively different from that ofintersubunitcontacts (C1–C4, C1–R1, and C1–R4). This difference may allow the transmission of information across subunit interfaces to be selectively regulated. Groups whose calculated pK or charge changes as a result of protein‐protein interactions have been identified and the results correlated with available information about their function. Both the 240s loop of the c chain and the region near the Zn(II) ion of the r chain contain clusters of ionizable groups whose calculated pK values change by relatively large amounts upon assembly. These pK changes in turn extend to regions of the protein remote from the interface. The possibility that networks of ionizable groups are involved in transmitting information between bin

ISSN:0887-3585    

DOI:10.1002/prot.340050108

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

年代:1989

数据来源: WILEY

ISSN:0887-3585    

DOI:10.1002/prot.340050109

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

年代:1989

数据来源: WILEY

摘要:

AbstractPrevious results from equilibrium and kinetic studies of the folding of bovine growth hormone (bGH) have demonstrated that bGH does not follow a simple two‐step folding mechanism. These results are summarized and interpreted according to the “molten globule” model. The molten globule state of bGH is characterized as a folding intermediate which largely a‐helical, retains a compact hydrodynamic radius, has packing of the aromatic side chains that is similar to the unfolded state, and possesses a solvent‐exposed hydrophobic surface along helix 106127 that readily leads as

ISSN:0887-3585    

DOI:10.1002/prot.340050110

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

年代:1989

数据来源: WILEY

ISSN:0887-3585    

DOI:10.1002/prot.340050101

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

年代:1989

数据来源: WILEY