CCME, a Nuclear-encoded Heme-binding Protein Involved in Cytochrome c Maturation in Plant Mitochondria

Abstract

The maturation of c-type cytochromes requires the covalent attachment of the heme cofactor to the apoprotein. For this process, plant mitochondria follow a pathway distinct from that of animal or yeast mitochondria, closer to that found in ␣-and ␥-proteobacteria. We report the first characterization of a nuclear-encoded component, namely AtCCME, the Arabidopsis thaliana orthologue of CcmE, a periplasmic heme chaperone in bacteria. AtCCME is targeted to mitochondria, and its N-terminal signal peptide is cleaved upon import. At-CCME is a peripheral protein of the mitochondrial inner membrane, and its major hydrophilic domain is oriented toward the intermembrane space. Although a At-CCME (Met 79 -Ser 256) is not fully able to complement an Escherichia coli CcmE mutant strain for bacterial holocytochrome c production, it is able to bind heme covalently through a conserved histidine, a feature previously shown for E. coli CcmE. Our results suggest that AtCCME is important for cytochrome c maturation in A. thaliana mitochondria and that its heme-binding function has been conserved evolutionary between land plant mitochondria and ␣-proteobacteria.

The Interaction of Covalently Bound Heme with the Cytochrome c Maturation Protein CcmE

“…The quality of the spectra is hampered by strong fluorescence. The spin state marker band, 3 , was observed faintly at ϳ1468 cm Ϫ1 for the reduced protein (Fig. 7, spectrum b), although it was clearly observed at 1493 cm Ϫ1 for the wild-type protein (Fig.…”

C-type cytochromes: diverse structures and biogenesis systems pose evolutionary problems

“…Unlike fungal, invertebrate and vertebrate cell mitochondria, these seem to use some components of the Ccm system (at least CcmA, CcmB, CcmC, CcmE and CcmF; Spielewoy et al 2001). If the analogy is drawn with the operation of the Ccm system in bacteria, then one might expect that there would be an intramolecular disulphide in an apocytochrome c in the intermembrane space of plant mitochondria.…”

Iron and Porphyrin Trafficking in Heme Biogenesis

“…It is likely that chaperones play a role in delivering heme from the site of synthesis to the sites of utilization. Heme chaperones that are important for cytochrome c biogenesis have been discovered in bacteria and plants (60,61). Although no heme chaperone has been identified in mammals, several known cytosolic heme-binding proteins may facilitate intracellular heme transfer.…”