title: Xylanase attachment to the cell wall of the hyperthermophilic bacterium Thermotoga maritima.
abstract: The cellular localization and processing of the endo-xylanases (1,4-beta-D-xylan-xylanohydrolase; EC 3.2.1.8) of the hyperthermophile Thermotoga maritima were investigated, in particular with respect to the unusual outer membrane ("toga") of this gram-negative bacterium. XynB (40 kDa) was detected in the periplasmic fraction of T. maritima cells and in the culture supernatant. XynA (120 kDa) was partially released to the surrounding medium, but most XynA remained cell associated. Immunogold labeling of thin sections revealed that cell-bound XynA was localized mainly in the outer membranes of T. maritima cells. Amino-terminal sequencing of purified membrane-bound XynA revealed processing of the signal peptide after the eighth residue, thereby leaving the hydrophobic core of the signal peptide attached to the enzyme. This mode of processing is reminiscent of type IV prepilin signal peptide cleavage. Removal of the entire XynA signal peptide was necessary for release from the cell because enzyme purified from the culture supernatant lacked 44 residues at the N terminus, including the hydrophobic part of the signal peptide. We conclude that toga association of XynA is mediated by residues 9 to 44 of the signal peptide. The biochemical and electron microscopic localization studies together with the amino-terminal processing data indicate that XynA is held at the cell surface of T. maritima via a hydrophobic peptide anchor, which is highly unusual for an outer membrane protein.
authors: Institut für Mikrobiologie und Genetik, Georg-August-Universität, Grisebachstr. 8, D-37077 Göttingen, Germany. wliebl@gwdg.de
authors: Wolfgang
authors: W
authors: Liebl
authors: Christoph
authors: C
authors: Winterhalter
authors: Wolfgang
authors: W
authors: Baumeister
authors: Martin
authors: M
authors: Armbrecht
authors: Michael
authors: M
authors: Valdez
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020124:Thermotoga maritima / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D001426:Bacterial Proteins; D010446:Peptide Fragments; D043364:Endo-1,4-beta Xylanases