title: Signal peptidase I-mediated processing of an engineered mammalian cytochrome b(5) precursor is an exocytoplasmic post-translocational event in Escherichia coli.
abstract: Proteins destined for translocation across the prokaryotic cytoplasmic membrane are synthesized as precursors carrying transient N-terminal extensions known as signal sequences. They facilitate initial engagement of precursor proteins with the sec-dependent translocase to initiate active threading of the polypeptide across the membrane. The translocated precursor is then processed by a transcytoplasmic signal peptidase anchored to the inner membrane. The temporal nature of cleavage of the signal sequence during pre-protein translocation has remained elusive. Using an engineered mammalian cytochrome b(5) precursor we demonstrate that the signal peptide processing in Escherichia coli is an event that can occur after almost complete exocytoplasmic translocation of the preprotein is accomplished. We discuss implications of the findings in light of the known working model of sec-dependent pre-protein translocon.
authors.affiliation: Institute of Biological Sciences, Aberystwyth University, Wales, UK. mak@aber.ac.uk
authors.forename: Naheed N
authors.initials: NN
authors.lastname: Kaderbhai
authors.forename: Victoria
authors.initials: V
authors.lastname: Harding
authors.forename: Mustak A
authors.initials: MA
authors.lastname: Kaderbhai
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D015786:Cytochromes b5 / Q000235:genetics / Q000378:metabolism*; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008322:Mammals; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D015202:Protein Engineering / Q000379:methods; D021382:Protein Sorting Signals / Q000502:physiology*; D021381:Protein Transport / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D004792:Enzyme Precursors; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D015786:Cytochromes b5; D012697:Serine Endopeptidases; C026515:type I signal peptidase