3uka | pdb_00003uka
CRYSTAL STRUCTURE OF UDP-galactopyranose mutase from Aspergillus fumigatus
Structural highlights
FunctionGLFA_ASPFM UDP-galactopyranose mutase, key flavoenzyme of galactofuranose metabolism that catalyzes the 6-to-5 ring contraction of UDP-galactopyranose to UDP-galactofuranose, the donor used by various galacto-furanosyltransferases (PubMed:16207086, PubMed:18552284, PubMed:22334662, PubMed:23036087, PubMed:25412209, PubMed:26836146). Controls the biosynthesis of galactomannan and galactofuranose containing glycoconjugates (PubMed:18552284). The flavin functions as nucleophile, forming a flavin-sugar adduct that facilitates galactose-ring opening and contraction (PubMed:26836146). The binding of UDP-galactopyranose induces profound conformational changes in the enzyme and two loops on opposite sides of the active site move toward each other by over 10 Angstroms to cover the substrate and create a closed active site (PubMed:22334662).[1] [2] [3] [4] [5] [6] Publication Abstract from PubMedUDP-galactopyranose mutase (UGM) is a flavin-containing enzyme that catalyzes the reversible conversion of UDP-galactopyranose (UDP-Galp) to UDP-galactofuranose (UDP-Galf). As in prokaryotic UGMs, the flavin needs to be reduced for the enzyme to be active. Here we present the first eukaryotic UGM structures from Aspergillus fumigatus (AfUGM). The structures are of UGM alone, with the substrate UDP-Galp and with the inhibitor UDP. Additionally, we report the structures of AfUGM bound to substrate with oxidized and educed flavin. These structures provide insight into substrate recognition and structural changes observed upon substrate binding involving the mobile loops and the critical arginine residues R182 and R327. Comparison with prokaryotic UGM reveals that despite low sequence identity with known prokaryotic UGMs the overall fold is largely conserved. Structural differences between prokaryotic UGM and AfUGM result from inserts in AfUGM. A notable difference from prokaryotic UGMs is that AfUGM contains a third flexible loop (loop III) above the si-face of the isoalloxazine ring that changes position depending on the redox state of the flavin cofactor. This loop flipping has not been observed in prokaryotic UGMs. In addition we have determined the crystals structures and steady-state kinetic constants of the reaction catalyzed by mutants R182K, R327K, R182A and R327A. These results support our hypothesis that R182 and R327 play important roles in stabilizing the diphosphates of the nucleotide sugar and help to facilitate the positioning of the galactose moiety for catalysis. Structural insight into the unique substrate binding mechanism and flavin redox state of UDP-galactopyranose mutase from Aspergillus fumigatus.,van Straaten KE, Routier FH, Sanders DA J Biol Chem. 2012 Feb 10. PMID:22334662[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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