RESEARCH ARTICLE In vitro reconstitution reveals major differences between human and bacterial cytochrome c synthases Molly C Sutherland1,2†*, Deanna L Mendez1†, Shalon E Babbitt1†‡, Dustin E Tillman1§, Olga Melnikov1, Nathan L Tran1, Noah T Prizant1, Andrea L Collier1, Robert G Kranz1* 1Department of Biology, Washington University in St. Louis, St. Louis, United States; 2Department of Biological Sciences, University of Delaware, Newark, United States Abstract Cytochromes c are ubiquitous heme proteins in mitochondria and bacteria, all possessing a CXXCH (CysXxxXxxCysHis) motif with covalently attached heme. We describe the first in vitro reconstitution of cytochrome c biogenesis using purified mitochondrial (HCCS) and bacterial (CcsBA) cytochrome c synthases. We employ apocytochrome c and peptide analogs containing CXXCH as substrates, examining recognition determinants, thioether attachment, and subsequent release and folding of cytochrome c. Peptide analogs reveal very different recognition requirements between HCCS and CcsBA. For HCCS, a minimal 16-mer peptide is required, *For correspondence: comprised of CXXCH and adjacent alpha helix 1, yet neither thiol is critical for recognition. For
[email protected] (MCS); bacterial CcsBA, both thiols and histidine are required, but not alpha helix 1. Heme attached
[email protected] (RGK) peptide analogs are not released from the HCCS active site; thus, folding is important in the release mechanism. Peptide analogs behave as inhibitors of cytochrome c biogenesis, paving the †These authors contributed equally to this work way for targeted control. Present address: ‡Pfizer, Chesterfield, United States; §Department of Molecular and Introduction Cellular Biology, Harvard University, Cambridge, United The structure of cytochrome c (cyt c), as well as its key function in electron transport for aerobic res- States piration, have been known for over half a century (Dickerson et al., 1971; Ernster and Schatz, 1981).