title: Determination of the Oligomeric State of SecYEG Protein Secretion Channel Complex Using in Vivo Photo- and Disulfide Cross-linking.
abstract: SecYEG protein of bacteria or Sec61αβγ of eukaryotes is a universally conserved heterotrimeric protein channel complex that accommodates the partitioning of membrane proteins into the lipid bilayer as well as the secretion of proteins to the trans side of the plasma or endoplasmic reticular membrane, respectively. SecYEG function is facilitated by cytosolic partners, mainly a nascent chain-ribosome complex or the SecA ATPase motor protein. Extensive efforts utilizing both biochemical and biophysical approaches have been made to determine whether SecYEG functions as a monomer or a dimer, but such approaches have often generated conflicting results. Here we have employed site-specific in vivo photo-cross-linking or cysteine cross-linking, along with co-immunoprecipitation or SecA footprinting techniques to readdress this issue. Our findings show that the SecY dimer to monomer ratio is relatively constant regardless of whether translocons are actively engaged with protein substrate or not. Under the former conditions the SecY dimer can be captured associated with a translocon-jammed substrate, indicative of SecY dimer function. Furthermore, SecA ATPase can be cross-linked to two copies of SecY when the complex contains a translocation intermediate. Collectively, our results suggest that SecYEG dimers are functional units of the translocon.
authors.affiliation: From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
authors.forename: Zeliang
authors.initials: Z
authors.lastname: Zheng
authors.affiliation: From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
authors.forename: Amy
authors.initials: A
authors.lastname: Blum
authors.affiliation: From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
authors.forename: Tithi
authors.initials: T
authors.lastname: Banerjee
authors.affiliation: From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
authors.forename: Qianyu
authors.initials: Q
authors.lastname: Wang
authors.affiliation: From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
authors.forename: Virginia
authors.initials: V
authors.lastname: Dantis
authors.affiliation: From the Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459. Electronic address: doliver@wesleyan.edu.
authors.forename: Donald
authors.initials: D
authors.lastname: Oliver
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000737:chemistry; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry; D008027:Light; D008958:Models, Molecular; D055668:Photochemical Processes; D011487:Protein Conformation; D055503:Protein Multimerization; D020124:Thermotoga maritima / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D004220:Disulfides; D003545:Cysteine
keywords: SecY; cysteine-mediated cross-linking; membrane protein; oligomer; photo-cross-linking; protein chimera; protein translocation; translocon jamming