title: A dual function for SecA in the assembly of single spanning membrane proteins in Escherichia coli.
abstract: The assembly of bacterial membrane proteins with large periplasmic loops is an intrinsically complex process because the SecY translocon has to coordinate the signal recognition particle-dependent targeting and integration of transmembrane domains with the SecA-dependent translocation of the periplasmic loop. The current model suggests that the ATP hydrolysis by SecA is required only if periplasmic loops larger than 30 amino acids have to be translocated. In agreement with this model, our data demonstrate that the signal recognition particle- and SecA-dependent multiple spanning membrane protein YidC becomes SecA-independent if the large periplasmic loop connecting transmembrane domains 1 and 2 is reduced to less than 30 amino acids. Strikingly, however, we were unable to render single spanning membrane proteins SecA-independent by reducing the length of their periplasmic loops. For these proteins, the complete assembly was always SecA-dependent even if the periplasmic loop was reduced to 13 amino acids. If, however, the 13-amino acid-long periplasmic loop was fused to a downstream transmembrane domain, SecA was no longer required for complete translocation. Although these data support the current model on the SecA dependence of multiple spanning membrane proteins, they indicate a novel function of SecA for the assembly of single spanning membrane proteins. This could suggest that single and multiple spanning membrane proteins are processed differently by the bacterial SecY translocon.
authors.affiliation: Institute for Biochemistry and Molecular Biology, Faculty for Medicine, University Freiburg, 79104 Freiburg, Federal Republic of Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Deitermann
authors.forename: Grit Sophie
authors.initials: GS
authors.lastname: Sprie
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Koch
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D018271:Signal Recognition Particle / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; D011994:Recombinant Proteins; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; D018271:Signal Recognition Particle; C412443:YIDC protein, E coli; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins