The Maltoporin-like channels (LamB porin) form a trimeric structure which facilitate the diffusion of maltodextrins and other sugars across the outer membrane of Gram-negative bacteria. The membrane channel is formed by an 18-strand antiparallel beta-barrel (18,22). Loop 3 folds into the core to constrict pore size. Long irregular loops are found on the extracelllular side, while short turns are in the periplasm.Tightly-bound water molecules are found in the eyelet of the passage, and only substrates that can displace and replace the broken hydrogen bonds are likely to enter the pore. In the MPR structure, loops 4,6, and 9 have the greatest mobility and are highly variable; these are postulated to attract maltodextrins.
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