1PIE

Crystal Structure of Lactococcus lactis Galactokinase Complexed with Galactose

Summary for 1PIE

• Entry DOI: 10.2210/pdb1pie/pdb
• Descriptor: Galactokinase, alpha-D-galactopyranose, PHOSPHATE ION, ... (4 entities in total)
• Functional Keywords: galactose, galactosemia, kinase, transferase
• Biological source: Lactococcus lactis
• Total number of polymer chains: 1
• Total formula weight: 46360.07

Authors

Thoden, J.B.,Holden, H.M. (deposition date: 2003-05-30, release date: 2003-09-23, Last modification date: 2024-02-14)

Primary citation

Thoden, J.B.,Holden, H.M.
Molecular Structure of Galactokinase
J.Biol.Chem., 278:33305-33311, 2003

PubMed Abstract: Galactokinase plays a key role in normal galactose metabolism by catalyzing the ATP-dependent phosphorylation of alpha-D-galactose to galactose 1-phosphate. In humans, mutations in the galactokinase gene can lead to the diseased state referred to as Type II galactosemia. Here we describe the three-dimensional structure of galactokinase from Lactococcus lactis determined to 2.1-A resolution. As expected from amino acid sequence alignments, galactokinase adopts a similar topology to that observed for members of the GHMP superfamily. The N-terminal domain is characterized by a five-stranded mixed beta-sheet while the C-terminal motif is dominated by two distinct four-stranded anti-parallel beta-sheets. The structure was solved in the presence of alpha-D-galactose and inorganic phosphate. These ligands are wedged between the N- and C-terminal domains. Amino acid side chains responsible for anchoring the sugar ligand to the protein include Arg36, Glu42, Asp45, Asp183, and Tyr233. Both Arg36 and Asp183 are strictly conserved in the amino acid sequences available in the literature thus far for galactokinases. Interestingly, the carboxylate side chain of Asp183 is positioned within 3.5 A of the C-1 hydroxyl group of galactose, whereas the guanidinium group of Arg36 is situated between both the C-1 hydroxyl group and the inorganic phosphate. Most likely these residues play key roles in catalysis. The structure of galactokinase described here serves as a model for understanding the functional consequences of point mutations known to result in Type II galactosemia in humans.

PubMed: 12796487
DOI: 10.1074/jbc.M304789200

Experimental method

X-RAY DIFFRACTION (2.1 Å)