A model of maltodextrin transport through the sugar-specific porin, LamB, based on deletion analysis.
LamB facilitates the uptake of maltose and maltodextrins across the bacterial outer membrane and acts as a general porin for small molecules. Using directed deletion mutagenesis we removed several regions of the LamB polypeptide and identified a polypeptide loop that both constricts the maltoporin channel and binds maltodextrins. In conjunction with a second sugar binding site that we identified at the rim of the channel, these data clarify, for the first time, the mechanism of transport through a substrate-specific porin. Furthermore, unlike the transverse loops of general porins, which originate from a central location in their primary structure, the loop that regulates LamB permeability originates from a C-terminal site. Thus LamB represents a second distinct class of porins in the bacterial outer membrane that is differently organized and separately evolved from OmpF-type, general porins.
Klebba
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PE
Unité de Programmation Moleculaire et Toxicologie Génétique CNRS URA 1444, Institut Pasteur, Paris, France.
Hofnung
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Charbit
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D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins; D001665:Binding Sites; D004926:Escherichia coli / Q000378:metabolism; D008320:Maltose / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011134:Polysaccharides / Q000378:metabolism*; D018272:Porins / Q000378:metabolism*; D011487:Protein Conformation; D011991:Receptors, Virus / Q000378:metabolism*
D001425:Bacterial Outer Membrane Proteins; D011134:Polysaccharides; D018272:Porins; D011991:Receptors, Virus; C016532:maltoporins; D008320:Maltose; C008315:maltodextrin