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Comparison of the closed conformation of the beta 1,4- galactosyltransferase-1 (beta 4Gal-T1) in the presence and absence of alpha-lactalbumin (LA)

  1. Author:
    Ramakrishnan, B.
    Qasba, P. K.

  2. Author Address

    NCI, CCR, LECB, Struct Glycobiol Sect, Bldg 469,Room 221, Frederick, MD 21702 USA NCI, CCR, LECB, Struct Glycobiol Sect, Frederick, MD 21702 USA NCI, CCR, LECB, SAIC Frederick Inc,Basic Res Program, Frederick, MD 21702 USA Qasba PK NCI, CCR, LECB, Struct Glycobiol Sect, Bldg 469,Room 221, Frederick, MD 21702 USA
    1. Year: 2003
  2. Journal: Journal of Biomolecular Structure & Dynamics
    1. 21
    2. 1
    3. Pages: 1-8
  4. Type of Article: Article
  1. Abstract:

    beta1,4-Galactosyltransferase (beta4Gal-T1) transfers galactose from UDP-galactose to N-acetylglucosamine (GlcNAc) in the presence of Mn2+ ion. However, in the presence of alpha-lactal- bumin (LA) it transfers Gal to glucose (Glc) instead to GlcNAc. Upon substrate binding, beta4Gal-T1 undergoes transition, from an open to a closed conformation. Although both the acceptor and donor substrates can induce the necessary conformational changes, the enzyme has been crystallized only in the closed conformation in the presence of its preferred donor, UDP-Gal. The closed conformation induced by the sugar acceptors or the less preferred donor substrates has been observed only when complexed with LA. The crystal structure of beta4Gal-T1 in the presence of UDP-Gal was previously determined at 2.8 Angstrom resolution. We report here the same structure at 2.3 Angstrom resolution, which provides a better description of this closed conformation. We have also further refined the structures of beta4Gal-T1.LA complexes containing the sugar acceptor and the less preferred sugar nucleotide donor substrates and compared the conformational. changes in the enzyme induced by substrates with and without LA. Based on the binding of UDP-sugar molecules, a rational hypothesis is proposed for the conformational changes induced by the donor substrate.

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