Overlapping Specificities of the Mitochondrial Cytochrome c and c1 Heme Lyases

Abstract

Heme attachment to the apoforms of fungal mitochondrial cytochrome c and c 1 requires the activity of cytochrome c and c 1 heme lyases (CCHL and CC 1 HL), which are enzymes with distinct substrate specificity. However, the presence of a single heme lyase in higher eukaryotes is suggestive of broader substrate specificity. Here, we demonstrate that yeast CCHL is active toward the non-cognate substrate apocytochrome c 1 , i.e. CCHL promotes low levels of apocytochrome c 1 conversion to its holoform in the absence of CC 1 HL. Moreover, that the single human heme lyase also displays a broader cytochrome specificity is evident from its ability to substitute for both yeast CCHL and CC 1 HL. Multicopy and genetic suppressors of the absence of CC 1 HL were isolated and their analysis revealed that the activity of CCHL toward cytochrome c 1 can be enhanced by: 1) reducing the abundance of the cognate substrate apocytochrome c, 2) increasing the accumulation of CCHL, 3) modifying the substrate-enzyme interaction through point mutations in CCHL or cytochrome c 1 , or 4) overexpressing Cyc2p, a protein known previously only as a mitochondrial biogenesis factor. Based on the functional interaction of Cyc2p with CCHL and the presence of a putative FAD-binding site in the protein, we hypothesize that Cyc2p controls the redox chemistry of the heme lyase reaction.

The F1F0-ATP Synthase Complex Influences the Assembly State of the Cytochrome bc1-Cytochrome Oxidase Supercomplex and Its Association with the TIM23 Machinery

“…Furthermore, the measured decrease in COX enzyme activities in the intact ⌬su g mitochondria would also argue that the effect in the cytochrome bc 1 -COX supercomplex in the absence of Su g (or Su e) is not because of an in vitro detergent artifact. Finally, Western blotting analysis of ⌬su g and ⌬su e mitochondria has indicated that the steady state levels of cytochrome c are markedly increased in the absence of Su g or Su e. An increased expression level of cytochrome c has been observed previously in other COX-mutant yeast strains (53,54), further supporting the conclusion here that the COX activity is compromised in the absence of subunits e and g of the F 1 F 0 -ATP synthase.…”

AtCCMH, an essential component of thec-type cytochrome maturation pathway inArabidopsismitochondria, interacts with apocytochromec

“…It would be interesting to investigate whether ERV1 could catalyze the formation of a disulfide bond in apocytochromes, thus making the reducing activity of proteins such as CCMH necessary. Indeed, Cyc2p, a flavoprotein was recently shown to interact with system III CCHL and proposed to be involved in the redox chemistry of the heme lyase reaction in yeast mitochondria (38). Further investigations of the function of CCMH might give clues toward the understanding of the yet unknown mechanisms controlling the intermembrane space redox state in mitochondria.…”

Pregenerative medicine: developmental paradigms in the biology of cardiovascular regeneration

“…Not surprisingly, defects in the mitochondrial respiratory chain lead to severe cardiomyopathies (diseases characterized by deterioration of myocardial function), since cardiomyocytes are exquisitely sensitive to changes in metabolic conditions (69). In mammals, holocytochrome c synthase, which is encoded by the gene Hccs on the X chromosome, converts cytochrome c and cytochrome c1 to their active forms by attaching a heme moiety (70). Drenckhahn and colleagues engineered a cardiac-specific Hccs knockout (68).…”