Extended cardiolipin anchorage to cytochrome c: a model for protein-mitochondrial membrane binding.
Two models have been proposed to explain the interaction of cytochrome c with cardiolipin (CL) vesicles. In one case, an acyl chain of the phospholipid accommodates into a hydrophobic channel of the protein located close the Asn52 residue, whereas the alternative model considers the insertion of the acyl chain in the region of the Met80-containing loop. In an attempt to clarify which proposal offers a more appropriate explanation of cytochrome c-CL binding, we have undertaken a spectroscopic and kinetic study of the wild type and the Asn52Ile mutant of iso-1-cytochrome c from yeast to investigate the interaction of cytochrome c with CL vesicles, considered here a model for the CL-containing mitochondrial membrane. Replacement of Asn52, an invariant residue located in a small helix segment of the protein, may provide data useful to gain novel information on which region of cytochrome c is involved in the binding reaction with CL vesicles. In agreement with our recent results revealing that two distinct transitions take place in the cytochrome c-CL binding reaction, data obtained here support a model in which two (instead of one, as considered so far) adjacent acyl chains of the liposome are inserted, one at each of the hydrophobic sites, into the same cytochrome c molecule to form the cytochrome c-CL complex.
Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università di Roma "Tor Vergata", Italy.
Federica
F
Sinibaldi
Barry D
BD
Howes
Maria Cristina
MC
Piro
Fabio
F
Polticelli
Cecilia
C
Bombelli
Tommaso
T
Ferri
Massimo
M
Coletta
Giulietta
G
Smulevich
Roberto
R
Santucci
D001665:Binding Sites; D002308:Cardiolipins / Q000737:chemistry*; D045304:Cytochromes c / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification; D007700:Kinetics; D051336:Mitochondrial Membranes / Q000737:chemistry*; D008958:Models, Molecular
D002308:Cardiolipins; D045304:Cytochromes c