title: Structural contribution of C-terminal segments of NuoL (ND5) and NuoM (ND4) subunits of complex I from Escherichia coli.
abstract: The proton-translocating NADH-quinone oxidoreductase (complex I/NDH-1) is a multisubunit enzymatic complex. It has a characteristic L-shaped form with two domains, a hydrophilic peripheral domain and a hydrophobic membrane domain. The membrane domain contains three antiporter-like subunits (NuoL, NuoM, and NuoN, Escherichia coli naming) that are considered to be involved in the proton translocation. Deletion of either NuoL or NuoM resulted in an incomplete assembly of NDH-1 and a total loss of the NADH-quinone oxidoreductase activity. We have truncated the C terminus segments of NuoM and NuoL by introducing STOP codons at different locations using site-directed mutagenesis of chromosomal DNA. Our results suggest an important structural role for the C-terminal segments of both subunits. The data further advocate that the elimination of the last transmembrane helix (TM14) of NuoM and the TM16 (at least C-terminal seven residues) or together with the HL helix and the TM15 of the NuoL subunit lead to reduced stability of the membrane arm and therefore of the whole NDH-1 complex. A region of NuoL critical for stability of NDH-1 architecture has been discussed.
authors.affiliation: Department of Molecular and Experimental Medicine, MEM-256, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Jesus
authors.initials: J
authors.lastname: Torres-Bacete
authors.forename: Prem Kumar
authors.initials: PK
authors.lastname: Sinha
authors.forename: Akemi
authors.initials: A
authors.lastname: Matsuno-Yagi
authors.forename: Takao
authors.initials: T
authors.lastname: Yagi
mesh_terms: D002876:Chromosomes, Bacterial / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004795:Enzyme Stability / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D016297:Mutagenesis, Site-Directed; D009245:NADH Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011522:Protons
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D011522:Protons; D009245:NADH Dehydrogenase; C479743:NuoL protein, E coli; C476247:NuoM protein, E coli