Comparative Analysis of Highly HomologousShewanellaCytochromesc5for Stability and Function

Homologous cytochromes c(5) from a mesophile, Shewanella amazonensis (SA cytc(5)), and a psychrophile, Shewanella violacea (SV cytc(5)), were compared to elucidate the molecular mechanisms underlying protein stability and function. Cyclic voltammetry revealed that the two proteins had the same redox potential value. Differential scanning calorimetry showed that SV cytc(5) was more stable than SA cytc(5) in an enthalpic manner. These results and the structure model of Shewanella oneidensis cytochrome c(5) indicated that hydrophobic heme environments in the two proteins are the same to maintain the same redox potential value, and that the intra-molecular interactions in SV cytc(5), perhaps involved in Lys-50 and Tyr-73, account for its higher stability. Electron transfer from SV cytc(5) to membrane proteins of S. violacea and S. amazonensis was faster than that from SA cytc(5), suggesting that solvent-exposed Lys-4 in SV cytc(5) is responsible for the faster association and dissociation between SV cytc(5) and its redox partner.