title: Structural characterization of the transmembrane domain from subunit e of yeast F1Fo-ATP synthase: a helical GXXXG motif located just under the micelle surface.
abstract: F1Fo-ATP synthase is a large multiprotein complex, including at least 10 subunits in the membrane-bound Fo-sector. One of these Fo proteins is subunit e (Su e), involved in the stable dimerization of F1Fo-ATP synthase, and required for the establishment of normal cristae membrane architecture. As a step toward enabling structure-function studies of the Fo-sector, the Su e transmembrane region was structurally characterized in micelles. Based on a series of NMR and CD (circular dichroism) studies, a structural model of the Su e/micelle complex was constructed, indicating Su e is largely helical, and emerges from the micelle with Arg20 near the phosphate head groups. Su e only adopts this folded conformation in the context of the micelle, and is essentially disordered in DMSO, water or trifluoroethanol/water. Within the micelle the C-terminal Ala10-Arg20 stretch is helical, while the region N-terminal may be transiently helical, based on negative CSI (chemical shift index) values. The Ala10-Arg20 helix contains the G14XXXG18 motif, which has been proposed to play an important role in dimer formation with another protein from the Fo-sector. The Gly on the C-terminal end of this motif (Gly18) is slightly more mobile than the more buried Gly14, based on NMR order parameter measurements (Gly14 S2 = 0.950; Gly18 S2 = 0.895). Only one Su e transmembrane peptide is bound per micelle, and micelles are 22-23 A in diameter, composed of 51 +/- 4 dodecylphosphocholine detergent molecules. Although there is no evidence for Su e homodimerization via the transmembrane domain, potentially synergistic roles for N-terminal (membrane) and C-terminal (soluble) domain interactions may still occur. Furthermore, the presence of a buried charged residue (Arg7) suggests there may be interactions with other Fo-sector protein(s) that stabilize this charge, and possibly drive the folding of the N-terminal 9 residues of the transmembrane domain.
authors.affiliation: Chemical Proteomics Facility at Marquette, Department of Chemistry, Marquette University, P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, USA.
authors.forename: Huili
authors.initials: H
authors.lastname: Yao
authors.forename: Rosemary A
authors.initials: RA
authors.lastname: Stuart
authors.forename: Sheng
authors.initials: S
authors.lastname: Cai
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Sem
mesh_terms: D000595:Amino Acid Sequence; D008823:Micelles; D008969:Molecular Sequence Data; D011487:Protein Conformation; D006180:Proton-Translocating ATPases / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D008823:Micelles; D006180:Proton-Translocating ATPases