title: Structure of subcomplex Iβ of mammalian respiratory complex I leads to new supernumerary subunit assignments.
abstract: Mitochondrial complex I (proton-pumping NADH:ubiquinone oxidoreductase) is an essential respiratory enzyme. Mammalian complex I contains 45 subunits: 14 conserved "core" subunits and 31 "supernumerary" subunits. The structure of Bos taurus complex I, determined to 5-Å resolution by electron cryomicroscopy, described the structure of the mammalian core enzyme and allowed the assignment of 14 supernumerary subunits. Here, we describe the 6.8-Å resolution X-ray crystallography structure of subcomplex Iβ, a large portion of the membrane domain of B. taurus complex I that contains two core subunits and a cohort of supernumerary subunits. By comparing the structures and composition of subcomplex Iβ and complex I, supported by comparisons with Yarrowia lipolytica complex I, we propose assignments for eight further supernumerary subunits in the structure. Our new assignments include two CHCH-domain containing subunits that contain disulfide bridges between CX9C motifs; they are processed by the Mia40 oxidative-folding pathway in the intermembrane space and probably stabilize the membrane domain. We also assign subunit B22, an LYR protein, to the matrix face of the membrane domain. We reveal that subunit B22 anchors an acyl carrier protein (ACP) to the complex, replicating the LYR protein-ACP structural module that was identified previously in the hydrophilic domain. Thus, we significantly extend knowledge of how the mammalian supernumerary subunits are arranged around the core enzyme, and provide insights into their roles in biogenesis and regulation.
authors.affiliation: Medical Research Council Mitochondrial Biology Unit, Cambridge, CB2 0XY, United Kingdom;
authors.forename: Jiapeng
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Medical Research Council Mitochondrial Biology Unit, Cambridge, CB2 0XY, United Kingdom;
authors.forename: Martin S
authors.initials: MS
authors.lastname: King
authors.affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 0QH, United Kingdom.
authors.forename: Minmin
authors.initials: M
authors.lastname: Yu
authors.affiliation: Medical Research Council Mitochondrial Biology Unit, Cambridge, CB2 0XY, United Kingdom;
authors.forename: Liron
authors.initials: L
authors.lastname: Klipcan
authors.affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 0QH, United Kingdom.
authors.forename: Andrew G W
authors.initials: AG
authors.lastname: Leslie
authors.affiliation: Medical Research Council Mitochondrial Biology Unit, Cambridge, CB2 0XY, United Kingdom; jh@mrc-mbu.cam.ac.uk.
authors.forename: Judy
authors.initials: J
authors.lastname: Hirst
mesh_terms: D000818:Animals; D002417:Cattle; D020285:Cryoelectron Microscopy; D042967:Electron Transport Complex I / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry*; D025062:Yarrowia
chemical_list: D021122:Protein Subunits; D042967:Electron Transport Complex I
keywords: CHCH domain; LYR protein; NADH:ubiquinone oxidoreductase; electron transport chain; mitochondria