Sugar Binding in Lactose Permease: Anomeric State of a Disaccharide Influences Binding Structure

Laboratory of Computational Biology, National Institutes of Health, Bldg 50, 50 South Drive, Bethesda, MD 20892, USA.
Journal of Molecular Biology (Impact Factor: 4.33). 05/2007; 367(5):1523-34. DOI: 10.1016/j.jmb.2007.02.001
Source: PubMed


Lactose permease in Escherichia coli (LacY) transports both anomeric states of disaccharides but has greater affinity for alpha-sugars. Molecular dynamics (MD) simulations are used to probe the protein-sugar interactions, binding structures, and global protein motions in response to sugar binding by investigating LacY (the experimental mutant and wild-type) embedded in a fully hydrated lipid bilayer. A total of 12 MD simulations of 20-25 ns each with beta(alpha)-d-galactopyranosyl-(1,1)-beta-d-galactopyranoside (betabeta-(Galp)(2)) and alphabeta-(Galp)(2) result in binding conformational families that depend on the anomeric state of the sugar. Both sugars strongly interact with Glu126 and alphabeta-(Galp)(2) has a greater affinity to this residue. Binding conformations are also seen that involve protein residues not observed in the crystal structure, as well as those involved in the proton translocation (Phe118, Asn119, Asn240, His322, Glu325, and Tyr350). Common to nearly all protein-sugar structures, water acts as a hydrogen bond bridge between the disaccharide and protein. The average binding energy is more attractive for alphabeta-(Galp)(2) than betabeta-(Galp)(2), i.e. -10.7(+/-0.7) and -3.1(+/-1.0) kcal/mol, respectively. Of the 12 helices in LacY, helix-IV is the least stable with betabeta-(Galp)(2) binding resulting in larger distortion than alphabeta-(Galp)(2).

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    • "Additional mutations in LacY that result in the enhancement of transport for other distinct sugars have been found and are well-documented (Brooker, Fiebig et al. 1985; Brooker and Wilson 1985; Brooker and Wilson 1985; Collins, Permuth et al. 1989; Franco, Eelkema et al. 1989; Olsen and Brooker 1989; Brooker 1990; King and Wilson 1990; Brooker 1991; Eelkema, O'Donnell et al. 1991; Gram and Brooker 1992; Goswitz and Brooker 1993; Olsen, Greene et al. 1993; Varela and Wilson 1996; Varela, Brooker et al. 1997; Varela, Wilson et al. 2000; Shinnick and Varela 2002). Computational and biophysical analyses have been useful in the elucidation of sugar binding properties and of the conformational changes that occur during lactose transport across the membrane (Park and Lee 2005; Kasho, Smirnova et al. 2006; Vadyvaloo, Smirnova et al. 2006; Yin, Jensen et al. 2006; Jensen, Yin et al. 2007; Klauda and Brooks 2007). In addition, studies of maltoporin (LamB) have been tremendously helpful in the elucidation the molecular basis of maltose transport across the membrane via outer membrane porin channels (Boos and Shuman 1998). "
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