title: Topology of the membrane-bound alkane hydroxylase of Pseudomonas oleovorans.
abstract: The Pseudomonas oleovorans alkane hydroxylase is an integral cytoplasmic membrane protein that is expressed and active in both Escherichia coli and P. oleovorans. Its primary sequence contains eight hydrophobic stretches that could span the membrane as alpha-helices. The topology of alkane hydroxylase was studied in E. coli using protein fusions linking different amino-terminal fragments of the alkane hydroxylase (AlkB) to alkaline phosphatase (PhoA) and to beta-galactosidase (LacZ). Four AlkB-PhoA fusions were constructed using transposon TnphoA. Site-directed mutagenesis was used to create PstI sites at 12 positions in AlkB. These sites were used to create AlkB-PhoA and AlkB-LacZ fusions. With respect to alkaline phosphatase and beta-galactosidase activity each set of AlkB-PhoA and AlkB-LacZ fusions revealed the expected complementary activities. At three positions, PhoA fusions were highly active, whereas the corresponding LacZ fusions were the least active. At all other positions the PhoA fusions were almost completely inactive, but the corresponding LacZ fusions were highly active. These data predict a model for alkane hydroxylase containing six transmembrane segments. In this model the amino terminus, two hydrophilic loops, and a large carboxyl-terminal domain are located in the cytoplasm. Only three very short loops near amino acid positions 52, 112, and 251 are exposed to the periplasm.
authors.affiliation: Department of Biochemistry, University of Groningen, The Netherlands.
authors.forename: J B
authors.initials: JB
authors.lastname: van Beilen
authors.forename: D
authors.initials: D
authors.lastname: Penninga
authors.forename: B
authors.initials: B
authors.lastname: Witholt
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D015153:Blotting, Western; D042926:Cytochrome P-450 CYP4A; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011549:Pseudomonas / Q000201:enzymology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D042926:Cytochrome P-450 CYP4A; D000469:Alkaline Phosphatase; D001616:beta-Galactosidase