Abstract
Homologous cytochromes c5 from a mesophile, Shewanella amazonensis (SA cytc5), and a psychrophile, Shewanella violacea (SV cytc5), 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 cytc5 was more stable than SA cytc5 in an enthalpic manner. These results and the structure model of Shewanella oneidensis cytochrome c5 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 cytc5, perhaps involved in Lys-50 and Tyr-73, account for its higher stability. Electron transfer from SV cytc5 to membrane proteins of S. violacea and S. amazonensis was faster than that from SA cytc5, suggesting that solvent-exposed Lys-4 in SV cytc5 is responsible for the faster association and dissociation between SV cytc5 and its redox partner.
