CcmI protein acts as an apocytochrome _c_ chaperone during cytochrome

ITQB Seminar

Title: CcmI protein acts as an apocytochrome _c_ chaperone during cytochrome
_c_ maturation

Speaker: Andreia F. Verissimo

Affiliation: Department of Biology, university of Pennsylvania, Philadelphia
(Andreia Verissimo is a former ITQB PhD student).     

Host: Manuela Pereira Auxiliary Inv. at Metalloenzymes and Molecular Bioenergetics 

Abstract

Cytochrome (cyt) c maturation (Ccm) is a sophisticated post-translational process. It occurs after translocation of apocyts c to the p side of energy transducing membranes, and forms stereo-specific thioether bonds between the vinyl groups of heme b (protoporphyrin IX-Fe) and the thiol groups of cysteines at their conserved heme binding sites. In many organisms this process involves up to ten (CcmABCDEFGHI and CcdA) membrane proteins. One of these proteins is CcmI, which has an N-terminal membrane-embedded domain with two transmembrane helices, and a large C-terminal periplasmic domain with protein-protein interaction motifs. Together with CcmF and CcmH, CcmI forms a multisubunit heme ligation complex. How the CcmFHI complex recognizes its apocyt c substrates remained unknown. Using Rhodobacter capsulatus apocyt c2 as a Ccm substrate, it is shown for the first time that CcmI binds apocyt c2, but not holocyt c2. Dissecting the different structural elements of both apocyt c2 and CcmI revealed that mainly the C-terminal portions of both CcmI and apocyt c2 mediate this binding, indicating that the CcmI subunit of the CcmFHI complex functions as an apocyt c chaperone during the Ccm process used by proteobacteria, archaea, mitochondria of plants and red algae.