Thermal destabilization mechanism of cytochrome c' from psychrophilic Shewanella violacea

Cytochrome c' is a nitric oxide (NO)-binding heme protein found in Gram negative bacteria. The thermal stability of psychrophilic Shewanella violacea cytochrome c' (SVCP) is lower than those of its homologues from other 2 psychrophilic Shewanella species, indicating that thermal destabilization mechanism for low-temperature adaptation accumulates in SVCP. In order to understand this mechanism at the amino acid level, here the stability and function of SVCP variants, modeled using the 2 homologues, were examined. The variants exhibited increased stability, and they bound NO similar to the wild type. The vulnerability as to the SVCP stability could be attributed to less hydrogen bond at the subunit interface, more flexible loop structure, and less salt bridge on the protein surface, which appear to be its destabilization mechanism. This study provides an example for controlling stability without spoiling function in psychrophilic proteins.