MalK forms a dimer independent of its assembly into the MalFGK2 ATP-binding cassette transporter of Escherichia coli.
The maltose transport complex (MTC) is a member of the ATP-binding cassette superfamily of membrane transport proteins and is a model for understanding the folding and assembly of hetero-oligomeric membrane protein complexes. The MTC is made up of two integral membrane proteins, MalF and MalG, and a peripheral membrane protein, MalK. These proteins associate with a stoichiometry of 1:1:2 to form the complex MalFGK2. In our studies of the oligomerization of this complex, we have shown that the ATP-binding component, MalK, forms a dimer in the absence of MalF and MalG. Epitope-tagged MalK coimmunoprecipitated with wild-type MalK, indicating that the MalK protein forms an oligomer. The relative amounts of tagged and wild-type MalK that were present in the whole cell extracts and in the immunoprecipitated complexes show that the MalK oligomer is a dimer. These hetero-oligomers can also be formed in vitro by mixing two extracts, each containing either tagged or wild-type MalK. The dimerization of MalK was also demonstrated in vivo using the bacteriophage lambda repressor fusion assay. The formation of a MalK dimer in the absence of MalF and MalG may represent an initial step in the assembly pathway of the MTC.
Department of Microbiology, University of Washington, Seattle, Washington 98195, USA.
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Kennedy
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Traxler
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D011485:Protein Binding
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; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; C461599:maltose transport system, E coli