The substitution of proline 35 by alanine in Rhodobacter capsulatus cytochrome c2 affects the overall protein stability but not the alkaline transition.
It was shown by Koshy et al. [1990, Proc. Natl Acad. Sci USA, 87, 8697-8701; 1994, Biochem. J., 299, 347-350] that the substitution of proline 30 by alanine (P30A) of Drosophila melanogaster and rat cytochromes c exhibited decreased stabilities in both the heme iron-methionine sulfur (Fe-S) bond and overall protein conformation. Now we have found that the stability properties of the equivalent mutant of Rhodobacter capsulatus cytochrome c2 (P35A) are somewhat different. Based on optical and NMR spectroscopies, the Rb.capsulatus P35A alkaline transition (pKalk) was found to be unchanged with respect to the wild type, suggesting that the mutation in Rb.capsulatus cytochrome c2 has little effect on the stability of the Fe-S bond. However, Rb.capsulatus conformational stability was found to be decreased by 1.6 kcal/mol in the oxidized state. The difference in the stability properties of the equivalent proline to alanine substitutions in various species underscores the importance of studying mutations in more than one species before drawing generalizations about the role of conserved residues in protein structure and function.
Caffrey
M S
MS
Department of Biochemistry, College of Pharmacy, University of Arizona, Tucson 85721, USA.
Gooley
P R
PR
Zhao
D
D
Meyer
T E
TE
Cusanovich
M A
MA
MacKenzie
N E
NE
D003574:Cytochrome c Group / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D045362:Cytochromes c2; D004578:Electron Spin Resonance Spectroscopy; D004795:Enzyme Stability / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D016297:Mutagenesis, Site-Directed; D016354:Rhodobacter capsulatus / Q000201:enzymology* / Q000235:genetics; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D003574:Cytochrome c Group; D045362:Cytochromes c2