7mri

Publication Abstract from PubMed

Naturally-occurring variants of human cytochrome c (Cytc) that induce thrombocytopenia IV occur within Omega-loop C (residues 40-57). These variants enhance the peroxidase activity of human Cytc apparently by facilitating access to the heme by destabilizing Omega-loops C and D (residues 70-85). Given the importance of peroxidase activity in the early stages of apoptosis, we identified three sites with the EVmutation algorithm in or near Omega-loop C that coevolve and differ between yeast iso-1-Cytc and human Cytc. We prepared iso-1-Cytc variants with all possible combinations of the S40T, V57I and N63T substitutions to determine if these residues decrease the peroxidase activity of iso-1-Cytc to that of human Cytc producing an effective off state for a peroxidase signaling switch. At pH 6 and above, all variants significantly decreased peroxidase activity. However, the correlation of peroxidase activity with local and global stability, expected if cooperative unfolding of Omega-loops C and D is required for peroxidase activity, was generally poor. The m-values derived from the guanidine hydrochloride dependence of the kinetics of imidazole binding to horse Cytc, which is well-characterized by native-state hydrogen exchange methods, and K72A/K73A/K79A iso-1-Cytc show that local structural fluctuations and not subglobal cooperative unfolding of Omega-loops C and D are sufficient to permit binding of a small molecule like peroxide to the heme. A 2.46 A structure of N63T iso-1-Cytc identifies a change to a hydrogen bond network linking Omega-loops C and D that could modulate the local fluctuations needed for the intrinsic peroxidase activity of Cytc.

Effect on intrinsic peroxidase activity of substituting coevolved residues from Omega-loop C of human cytochrome c into yeast iso-1-cytochrome c.,Frederick AK, Thompson SL, Vakharia ZM, Cherney MM, Lei H, Evenson G, Bowler BE J Inorg Biochem. 2022 Jul;232:111819. doi: 10.1016/j.jinorgbio.2022.111819. Epub , 2022 Apr 6. PMID:35428021^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.