Biogenesis of cytochrome b6 in photosynthetic membranes.
In chloroplasts, binding of a c'-heme to cytochrome b(6) on the stromal side of the thylakoid membranes requires a specific mechanism distinct from the one at work for c-heme binding to cytochromes f and c(6) on the lumenal side of membranes. Here, we show that the major protein components of this pathway, the CCBs, are bona fide transmembrane proteins. We demonstrate their association in a series of hetero-oligomeric complexes, some of which interact transiently with cytochrome b(6) in the process of heme delivery to the apoprotein. In addition, we provide preliminary evidence for functional assembly of cytochrome b(6)f complexes even in the absence of c'-heme binding to cytochrome b(6). Finally, we present a sequential model for apo- to holo-cytochrome b(6) maturation integrated within the assembly pathway of b(6)f complexes in the thylakoid membranes.
Saint-Marcoux
Denis
D
Centre National de la Recherche Scientifique, UMR 7141, Physiologie Membranaire et Moléculaire du Chloroplaste, Institut de Biologie Physico-Chimique, 75005 Paris, France.
Wollman
Francis-André
FA
de Vitry
Catherine
C
D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D045347:Cytochromes b6 / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D019281:Dimerization; D004586:Electrophoresis; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D020524:Thylakoids / Q000201:enzymology*; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000378:metabolism
D045347:Cytochromes b6; D008565:Membrane Proteins; D015800:Protozoan Proteins; D025801:Ubiquitin