title: Conformational properties of cardiolipin-bound cytochrome c.
abstract: Interactions of cytochrome c (cyt c) with cardiolipin (CL) are important for both electron transfer and apoptotic functions of this protein. A sluggish peroxidase in its native state, when bound to CL, cyt c catalyzes CL peroxidation, which contributes to the protein apoptotic release. The heterogeneous CL-bound cyt c ensemble is difficult to characterize with traditional structural methods and ensemble-averaged probes. We have employed time-resolved FRET measurements to evaluate structural properties of the CL-bound protein in four dansyl (Dns)-labeled variants of horse heart cyt c. The Dns decay curves and extracted Dns-to-heme distance distributions P(r) reveal a conformational diversity of the CL-bound cyt c ensemble with distinct populations of the polypeptide structures that vary in their degree of protein unfolding. A fraction of the ensemble is substantially unfolded, with Dns-to-heme distances resembling those in the guanidine hydrochloride-denatured state. These largely open cyt c structures likely dominate the peroxidase activity of the CL-bound cyt c ensemble. Site variations in P(r) distributions uncover structural features of the CL-bound cyt c, rationalize previous findings, and implicate the prime role of electrostatic interactions, particularly with the protein C terminus, in the CL-induced unfolding.
authors.affiliation: Department of Chemistry, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Jonas
authors.initials: J
authors.lastname: Hanske
authors.forename: Jason R
authors.initials: JR
authors.lastname: Toffey
authors.forename: Anna M
authors.initials: AM
authors.lastname: Morenz
authors.forename: Amber J
authors.initials: AJ
authors.lastname: Bonilla
authors.forename: Katherine H
authors.initials: KH
authors.lastname: Schiavoni
authors.forename: Ekaterina V
authors.initials: EV
authors.lastname: Pletneva
mesh_terms: D000818:Animals; D002308:Cardiolipins / Q000737:chemistry* / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D005454:Fluorescence Polarization; D031541:Fluorescence Resonance Energy Transfer; D006736:Horses / Q000378:metabolism; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009994:Osmolar Concentration; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D002308:Cardiolipins; D050505:Mutant Proteins; D045304:Cytochromes c