1f6s
CRYSTAL STRUCTURE OF BOVINE ALPHA-LACTALBUMIN
Structural highlights
FunctionLALBA_BOVIN Regulatory subunit of lactose synthase, changes the substrate specificity of galactosyltransferase in the mammary gland making glucose a good acceptor substrate for this enzyme. This enables LS to synthesize lactose, the major carbohydrate component of milk. In other tissues, galactosyltransferase transfers galactose onto the N-acetylglucosamine of the oligosaccharide chains in glycoproteins. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedHigh affinity binding of Ca(2+) to alpha-lactalbumin (LA) stabilizes the native structure and is required for the efficient generation of native protein with correct disulfide bonds from the reduced denatured state. A progressive increase in affinity of LA conformers for Ca(2+) as they develop increasingly native structures can account for the tendency of the apo form to assume a molten globule state and the large acceleration of folding by Ca(2+). To investigate the effect of calcium on structure of bovine LA, x-ray structures have been determined for crystals of the apo and holo forms at 2.2-A resolution. In both crystal forms, which were grown at high ionic strength, the protein is in a similar global native conformation consisting of alpha-helical and beta-subdomains separated by a cleft. Even though alternative cations and Ca(2+) liganding solvent molecules are absent, removal of Ca(2+) has only minor effects on the structure of the metal-binding site and a structural change was observed in the cleft on the opposite face of the molecule adjoining Tyr(103) of the helical lobe and Gln(54) of the beta-lobe. Changes include increased separation of the lobes, loss of a buried solvent molecule near the Ca(2+)-binding site, and the replacement of inter- and intra-lobe H-bonds of Tyr(103) by interactions with new immobilized water molecules. The more open cleft structure in the apo protein appears to be an effect of calcium binding transmitted via a change in orientation of helix H3 relative to the beta-lobe to the inter-lobe interface. Calcium is well known to promote the folding of LA. The results from the comparison of apo and holo structures of LA provide high resolution structural evidence that the acceleration of folding by Ca(2+) is mediated by an effect on interactions between the two subdomains. Crystal structures of apo- and holo-bovine alpha-lactalbumin at 2. 2-A resolution reveal an effect of calcium on inter-lobe interactions.,Chrysina ED, Brew K, Acharya KR J Biol Chem. 2000 Nov 24;275(47):37021-9. PMID:10896943[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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