Structural model of MalK, the ABC subunit of the maltose transporter of Escherichia coli: implications for mal gene regulation, inducer exclusion, and subunit assembly.
We are presenting a three-dimensional model of MalK, the ABC subunit of the maltose transporter from Escherichia coli and Salmonella typhimurium. It is based on the recently published crystal structure of the closely related Thermococcus litoralis MalK. The model was used to identify the position of mutations affecting the different functions of the ABC subunit. Six malK point mutations were isolated specifically affecting the interaction with MalT, the transcriptional regulator of the maltose system. They were mapped on the structural model and define a MalT interaction site that is located on an exposed surface of the C-terminal regulatory domain. Published point mutations that confer an inducer exclusion insensitive phenotype form a patch adjacent to and oriented perpendicularly to the MalT interaction site. Three sequence motifs were identified and visualized that are highly conserved among ABC subunits with extended C termini. They form a subdomain between the regulatory and ATPase domain and might play an important role in signal transduction events between these two domains. Mutations in this domain remain fully active in MalT regulation but cause transport defects. In addition, amino acids that have previously been shown to be involved in the interaction with the transmembranous subunits MalF and MalG and that fall into the highly conserved N-terminal ATPase domain were visualized. The validity of the modeled MalK structure was verified by structure-directed mutagenesis of amino acids located within the proposed MalK-MalT interaction site.
Böhm
Alex
A
Department of Biology, Universität Konstanz, 78457 Konstanz, Germany.
Diez
Joachim
J
Diederichs
Kay
K
Welte
Wolfram
W
Boos
Winfried
W
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D008320:Maltose / Q000378:metabolism; D058619:Maltose-Binding Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D017354:Point Mutation; D011487:Protein Conformation; D021122:Protein Subunits; D015183:Restriction Mapping; D012486:Salmonella typhimurium / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D001616:beta-Galactosidase / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C079123:MalG protein, E coli; C068021:MalK protein, Bacteria; C489398:MalK protein, E coli; C489399:MalK protein, Salmonella typhimurium; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D021122:Protein Subunits; C461599:maltose transport system, E coli; D008320:Maltose; D001616:beta-Galactosidase; D000251:Adenosine Triphosphatases