Document Detail

Effects of mutations in plastocyanin on the kinetics of the protein rearrangement gating the electron-transfer reaction with zinc cytochrome c. Analysis of the rearrangement pathway.
MedLine Citation:
PMID:  8987979     Owner:  NLM     Status:  MEDLINE    
We study, by flash kinetic spectrophotometry on the microsecond time scale, the effects of ionic strength and viscosity on the kinetics of oxidative quenching of the triplet state of zinc cytochrome c (3Zncyt) by the wild-type form and the following nine mutants of cupriplastocyanin: Leu12Glu, Leu12Asn, Phe35Tyr, Gln88Glu, Tyr83Phe, Tyr83His, Asp42Asn, Glu43Asn, and the double mutant Glu59Lys/Glu60Gln. The unimolecular rate constants for the quenching reactions within the persistent diprotein complex, which predominates at low ionic strengths, and within the transient diprotein complex, which is involved at higher ionic strengths, are equal irrespective of the mutation. Evidently, the two complexes are the same. In both reactions, the rate-limiting step is rearrangement of the diprotein complex from a configuration optimal for docking to the one optimal for the subsequent electron-transfer step, which is fast. We investigate the effects of plastocyanin mutations on this rearrangement, which gates the overall electron-transfer reaction. Conversion of the carboxylate anions into amide groups in the lower acidic cluster (residues 42 and 43), replacement of Tyr83 with other aromatic residues, and mutations in the hydrophobic patch in plastocyanin do not significantly affect the rearrangement. Conversion of a pair of carboxylate anions into a cationic and a neutral residue in the upper acidic cluster (residues 59 and 60) impedes the rearrangement. Creation of an anion at position 88, between the upper acidic cluster and the hydrophobic patch, facilitates the rearrangement. The rate constant for the rearrangement smoothly decreases as the solution viscosity increases, irrespective of the mutation. Fittings of this dependence to the modified Kramers's equation and to an empirical equation show that zinc cytochrome c follows the same trajectory on the surfaces of all the plastocyanin mutants but that the obstacles along the way vary as mutations alter the electrostatic potential. Mutations that affect protein association (i.e., change the binding constant) do not necessarily affect the reaction between the associated proteins (i.e., the rate constant) and vice versa. All of the kinetic and thermodynamic effects and noneffects of mutations consistently indicate that in the protein rearrangement the basic patch of zinc cytochrome c moves from a position between the two acidic clusters to a position at or near the upper acidic cluster.
M M Crnogorac; C Shen; S Young; O Hansson; N M Kostić
Related Documents :
21360819 - 2-amino-3,4,5-trimethoxybenzophenones as potent tubulin polymerization inhibitors.
22842709 - Expanded substrate scope and catalyst optimization for the catalytic kinetic resolution...
1390629 - Binding of dicyclohexylcarbodiimide to aspartate-155 or glutamate-166 of cytochrome b6 ...
240679 - Bacterial respiration-linked proton translocation and its relationship to respiratory-c...
9136869 - Reduced oxy intermediate observed in d251n cytochrome p450cam.
10806389 - Flexibility and stability of the structure of cytochromes p450 3a4 and bm-3.
24892979 - Crowded milieu prevents fibrillation of hen egg white lysozyme with retention of enzyma...
16122579 - Alpha-aminoalkylphosphonates as a tool in experimental optimisation of p1 side chain sh...
24900289 - Identification of potent and selective glucosylceramide synthase inhibitors from a libr...
Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  35     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1996 Dec 
Date Detail:
Created Date:  1997-01-30     Completed Date:  1997-01-30     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  16465-74     Citation Subset:  IM    
Department of Chemistry, Iowa State University, Ames 50011, USA.
Export Citation:
APA/MLA Format     Download EndNote     Download BibTex
MeSH Terms
Binding Sites
Cytochrome c Group / chemistry,  metabolism*
Cytochromes c*
Electron Transport
Models, Molecular
Mutagenesis, Site-Directed
Osmolar Concentration
Plastocyanin / chemistry,  genetics*,  metabolism*
Point Mutation
Protein Conformation
Static Electricity
Reg. No./Substance:
0/Cytochrome c Group; 0/zinc cytochrome c; 9007-43-6/Cytochromes c; 9014-09-9/Plastocyanin

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

Previous Document:  Combinatorial mutagenesis and structural simulations in the environment of the redox-active tyrosine...
Next Document:  Elimination of the hydrolytic water molecule in a class A beta-lactamase mutant: crystal structure a...