Hartley Andrew, Glynn Steven E, Barynin Vladimir, Baker Patrick J, Sedelnikova Svetlana E, Verhees Corné, de Geus Daniel, van der Oost John, Timson David J, Reece Richard J, Rice David W
Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
J Mol Biol. 2004 Mar 19;337(2):387-98. doi: 10.1016/j.jmb.2004.01.043.
Galactokinase (GalK) catalyses the first step of the Leloir pathway of galactose metabolism, the ATP-dependent phosphorylation of galactose to galactose-1-phosphate. In man, defects in galactose metabolism can result in disorders with severe clinical consequences, and deficiencies in galactokinase have been linked with the development of cataracts within the first few months of life. The crystal structure of GalK from Pyrococcus furiosus in complex with MgADP and galactose has been determined to 2.9 A resolution to provide insights into the substrate specificity and catalytic mechanism of the enzyme. The structure consists of two domains with the active site in a cleft at the domain interface. Inspection of the substrate binding pocket identifies the amino acid residues involved in galactose and nucleotide binding and points to both structural and mechanistic similarities with other enzymes of the GHMP kinase superfamily to which GalK belongs. Comparison of the sequence of the Gal3p inducer protein, which is related to GalK and which forms part of the transcriptional activation of the GAL gene cluster in the yeast Saccharomyces cerevisiae, has led to an understanding of the molecular basis of galactose and nucleotide recognition. Finally, the structure has enabled us to further our understanding on the functional consequences of mutations in human GalK which cause galactosemia.
半乳糖激酶（GalK）催化半乳糖代谢的Leloir途径的第一步，即ATP依赖的半乳糖磷酸化生成1-磷酸半乳糖。在人类中，半乳糖代谢缺陷可导致具有严重临床后果的疾病，而半乳糖激酶缺乏与出生后最初几个月内白内障的发生有关。已确定嗜热栖热菌（Pyrococcus furiosus）的GalK与MgADP和半乳糖复合物的晶体结构，分辨率为2.9埃，以深入了解该酶的底物特异性和催化机制。该结构由两个结构域组成，活性位点位于结构域界面的裂隙中。对底物结合口袋的检查确定了参与半乳糖和核苷酸结合的氨基酸残基，并指出与GalK所属的GHMP激酶超家族的其他酶在结构和机制上的相似性。对与GalK相关且构成酿酒酵母（Saccharomyces cerevisiae）GAL基因簇转录激活一部分的Gal3p诱导蛋白序列的比较，有助于理解半乳糖和核苷酸识别的分子基础。最后，该结构使我们能够进一步了解导致半乳糖血症的人类GalK突变的功能后果。
