THE SUBSTITUTION OF PROLINE-35 BY ALANINE IN RHODOBACTER-CAPSULATUS CYTOCHROME-C(2) 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 proli ne 30 by alanine (P30A) of Drosophila melanogaster and rat cytochromes c exhibited decreased stabilities in both the heme iron-methionine su lfur (Fe-S) bond and overall protein conformation, Now we have found t hat the stability properties of the equivalent mutant of Rhodobacter c apsulatus cytochrome c(2) (P35A) are somewhat different, Based on opti cal and NMR spectroscopies, the Rb. capsulatus P35A alkaline transitio n (PKalk) was found to be unchanged with respect to the wild type, sug gesting that the mutation in Rb. capsulatus cytochrome c(2) has little effect on the stability of the Fe-S bond. However, Rb. capsulatus con formational stability was found to be decreased by 1.6 kcal/mol in the oxidized state, The difference in the stability properties of the equ ivalent proline to alanine substitutions in various species underscore s the importance of studying mutations in more than one species before drawing generalizations about the role of conserved residues in prote in structure and function.