title: Periplasmic maltose- and glucose-binding protein activities in cell-free extracts of Thermotoga maritima.
abstract: In this study, high-affinity maltose- and glucose-binding activities in cell-free extracts of Thermotoga maritima were detected; these activities were distinct and specific. At the gross level, the expression of binding-protein activities was repressed by growth of T. maritima in the presence of the cognate sugar. Growth of the organism in the presence of maltose reduced maltose-binding activity but not glucose-binding activity, while growth in the presence of glucose reduced glucose-binding activity but not maltose-binding activity. In competition assays, these binding activities showed distinct patterns of substrate specificity: whereas the maltose-binding activity showed specificity for alpha-linked glucosides, the glucose-binding activity showed a broader specificity. All maltose- and glucose-binding activity was found in the supernatant retrieved following centrifugation (100,000 g) of the cell-free extracts prepared by French-pressure-cell treatment; no activity was found in an octyl-glucoside-treated extract of the membrane fraction. The maltose-binding-protein activity was recovered from the periplasmic fraction by selective release of the periplasmic contents of T. maritima cells using a newly developed freeze-thaw procedure. Annotation of the complete genome sequence of T. maritima suggests that there may be at least two maltose-binding proteins, MalE1 and MalE2, encoded in the genome. The maltose-binding activity corresponded to a protein of 43 kDa, which was consistent in size with either of the putative proteins. These data demonstrate that the hyperthermophilic bacterium T. maritima possesses separate maltose- and glucose-binding-protein activities that are freely soluble in its periplasm, in contrast to the membrane-bound sugar-binding proteins found in archaeal hyperthermophiles.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125, USA1.
authors.forename: Dhaval
authors.initials: D
authors.lastname: Nanavati
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125, USA1.
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Noll
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-3125, USA1.
authors.forename: Antonio H
authors.initials: AH
authors.lastname: Romano
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D003470:Culture Media; D004586:Electrophoresis; D005947:Glucose / Q000378:metabolism*; D008320:Maltose / Q000378:metabolism*; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D019897:Periplasm / Q000378:metabolism*; D013696:Temperature; D020124:Thermotoga maritima / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D003470:Culture Media; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D008320:Maltose; D005947:Glucose