title: Leaderless polypeptides efficiently extracted from whole cells by osmotic shock.
abstract: Three molecular foldases, DsbA, DsbC, and rotamase (ppiA), exhibited the unusual property of accumulating in an osmotically sensitive cellular compartment of Escherichia coli when their signal sequences were precisely removed by mutation. A mammalian protein, interleukin-1 (IL-1) receptor antagonist, behaved in a similar fashion in E. coli when its native signal sequence was deleted. These leaderless mutants (but not two control proteins overexpressed in the same system) were quantitatively extractable from whole cells by a variety of methods generally employed in the recovery of periplasmic proteins. A series of biochemical and genetic experiments showed that (i) leaderless DsbA (but not the wild type) was retained in a nonperiplasmic location; (ii) beta-galactosidase fusions to leaderless DsbA (but not to the wild type) exhibited efficient alpha complementation; (iii) none of the leaderless mutant proteins were substantially associated with cell membranes, even when they were overexpressed in cells; and (iv) leaderless DsbA was not transported to an osmotically sensitive compartment via a secA- or ftsZ-dependent mechanism. The observation that these proteins transit to some privileged cellular location by a previously undescribed mechanism(s)--absent their normal mode of (signal sequence-dependent) translocation--was unexpected. DsbA, rotamase, and IL-1, whose tertiary structures are known, appear to be structurally unrelated proteins. Despite a lack of obvious homologies, these proteins apparently have a common mechanism for intracellular localization. As this (putative) bacterial mechanism efficiently recognizes proteins of mammalian origin, it must be well conserved across evolutionary boundaries.
authors.affiliation: Department of Molecular & Cell Biology, Celtrix Pharmaceuticals, Santa Clara, California 95054, USA.
authors.forename: Y R
authors.initials: YR
authors.lastname: Thorstenson
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: P S
authors.initials: PS
authors.lastname: Olson
authors.forename: D
authors.initials: D
authors.lastname: Mascarenhas
mesh_terms: D000591:Amino Acid Isomerases / Q000032:analysis* / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000032:analysis* / Q000235:genetics; D002352:Carrier Proteins / Q000032:analysis* / Q000235:genetics; D002458:Cell Fractionation; D002462:Cell Membrane / Q000737:chemistry; D002473:Cell Wall / Q000737:chemistry; D003593:Cytoplasm / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007535:Isomerases / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009997:Osmotic Pressure; D019696:Peptidylprolyl Isomerase; D019704:Protein Disulfide-Isomerases; D017510:Protein Folding; D021382:Protein Sorting Signals / Q000502:physiology; D017472:Receptors, Interleukin-1 / Q000037:antagonists & inhibitors; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012795:Sialoglycoproteins / Q000032:analysis
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C507763:IL1RN protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D021382:Protein Sorting Signals; D017472:Receptors, Interleukin-1; D011993:Recombinant Fusion Proteins; D012795:Sialoglycoproteins; D007535:Isomerases; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase; D019704:Protein Disulfide-Isomerases