title: Site-directed mutagenesis of Phe 97 to Glu in amicyanin alters the electronic coupling for interprotein electron transfer from quinol methylamine dehydrogenase.
abstract: Conversion by site-directed mutagenesis of Phe 97 of amicyanin to Glu significantly decreases the rate constant for the electron-transfer reaction from the quinol form of methylamine dehydrogenase to amicyanin. It is shown that the DeltaG degrees and reorganizational energy (lambda) associated with the electron-transfer reaction are unaffected by the mutation and that the decrease in the electron-transfer rate is attributable completely to a decrease in the electronic coupling matrix element (HAB). Phe 97 is not a part of the predicted pathway for electron-transfer from the tryptophan tryptophylquinone cofactor of MADH to the copper of amicyanin. The most likely explanation for these results is that the mutation of this residue at the protein-protein interface causes an increase in the interprotein distance within the protein complex. The change in distance necessary to cause the observed reduction of HAB is calculated assuming a range of beta values, and assuming either solely a direct distance dependence or a pathway dependence, for the long-range electron-transfer reaction. Thermodynamic analysis of the association constants for complex formation reveal that the reaction with the mutant amicyanin exhibits a large positive change in heat capacity whereas this is not observed in the reaction with the wild-type. This may be explained by the replacement of a hydrophobic residue with a polar residue at what is normally a hydrophobic protein-protein interface. The impact of these results on possible explanations for the relatively large reorganizational energy associated with this interprotein electron-transfer reaction is also discussed.
authors.affiliation: Department of Biochemistry, The University of Mississippi Medical Center, Jackson 39216-4505, USA. davidson@fiona.umsmed.edu
authors.forename: V L
authors.initials: VL
authors.lastname: Davidson
authors.forename: L H
authors.initials: LH
authors.lastname: Jones
authors.forename: Z
authors.initials: Z
authors.lastname: Zhu
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004579:Electron Transport; D018698:Glutamic Acid / Q000235:genetics*; D008667:Metalloproteins / Q000235:genetics; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000201:enzymology / Q000378:metabolism*; D010649:Phenylalanine / Q000235:genetics*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D008667:Metalloproteins; C017079:mauC protein, Methylobacterium extorquens; D018698:Glutamic Acid; D010649:Phenylalanine; C021567:methylamine dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors