Ramakrishnan Boopathy, Boeggeman Elizabeth, Ramasamy Velavan, Qasba Pradman K
Structural Glycobiology Section, Laboratory of Experimental and Computational Biology, Center for Cancer Research, NCI-Frederick, MD 21702, USA.
Curr Opin Struct Biol. 2004 Oct;14(5):593-600. doi: 10.1016/j.sbi.2004.09.006.
Beta-1,4-galactosyltransferase-1, a housekeeping enzyme that functions in the synthesis of glycoconjugates, has two flexible loops, one short and one long. Upon binding a metal ion and UDP-galactose, the loops change from an open to a closed conformation, repositioning residues to lock the ligands in place. Residues at the N-terminal region of the long loop form the metal-binding site and those at the C-terminal region form a helix, which becomes part of the binding site for the oligosaccharide acceptor; the remaining residues cover the bound sugar-nucleotide. After binding of the oligosaccharide acceptor and transfer of the galactose moiety, the product disaccharide unit is ejected and the enzyme returns to the open conformation, repeating the catalytic cycle.
β-1,4-半乳糖基转移酶-1是一种参与糖缀合物合成的管家酶，它有两个柔性环，一个短环和一个长环。在结合金属离子和UDP-半乳糖后，这些环从开放构象转变为闭合构象，重新定位残基以将配体锁定在适当位置。长环N端区域的残基形成金属结合位点，C端区域的残基形成一个螺旋，该螺旋成为寡糖受体结合位点的一部分；其余残基覆盖结合的糖核苷酸。在寡糖受体结合和半乳糖部分转移后，产物二糖单元被排出，酶恢复到开放构象，重复催化循环。
