Co-translational protein targeting catalyzed by the Escherichia coli signal recognition particle and its receptor.
The Ffh-4.5S ribonucleoprotein particle (RNP) and FtsY from Escherichia coli are homologous to essential components of the mammalian signal recognition particle (SRP) and SRP receptor, respectively. The ability of these E. coli components to function in a bona fide co-translational targeting pathway remains unclear. Here we demonstrate that the Ffh-4.5S RNP and FtsY can efficiently replace their mammalian counterparts in targeting nascent secretory proteins to microsomal membranes in vitro. Targeting in the heterologous system requires a hydrophobic signal sequence, utilizes GTP and, moreover, occurs co-translationally. Unlike mammalian SRP, however, the Ffh-4.5S RNP is unable to arrest translational elongation, which results in a narrow time window for the ribosome nascent chain to interact productively with the membrane-bound translocation machinery. The highly negatively charged N-terminal domain of FtsY, which is a conserved feature among prokaryotic SRP receptor homologs, is important for translocation and acts to localize the protein to the membrane. Our data illustrate the extreme functional conservation between prokaryotic and eukaryotic SRP and SRP receptors and suggest that the basic mechanism of co-translational protein targeting is conserved between bacteria and mammals.
Powers
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Department of Biochemistry and Biophysics, University of California, School of Medicine, San Francisco 94143, USA. tpowers@socrates.ucsf.edu
Walter
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D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001692:Biological Transport; D004285:Dogs; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics; D029968:Escherichia coli Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D000072235:Mating Factor; D008565:Membrane Proteins / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D010179:Pancreas; D010441:Peptide Chain Elongation, Translational / Q000502:physiology; D010455:Peptides / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology; D011506:Proteins / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000378:metabolism*; D018000:Receptors, Peptide / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000378:metabolism*; D001618:beta-Lactamases / Q000378:metabolism
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C082931:Ffh protein, E coli; C087406:FtsY protein, Bacteria; D008565:Membrane Proteins; D010455:Peptides; D011498:Protein Precursors; D011506:Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D018271:Signal Recognition Particle; C036318:signal peptide receptor; D000072235:Mating Factor; C017671:preprolactin; D006160:Guanosine Triphosphate; D011388:Prolactin; D001618:beta-Lactamases