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EMBO J. 1994 Oct 3;13(19):4670-5.

A model of maltodextrin transport through the sugar-specific porin, LamB, based on deletion analysis.

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Unité de Programmation Moleculaire et Toxicologie Génétique CNRS URA 1444, Institut Pasteur, Paris, France.


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.

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