The X-ray crystal structures of human alpha-phosphomannomutase 1 reveal the structural basis of congenital disorder of glycosylation type 1a.
Congenital disorder of glycosylation type 1a (CDG-1a) is a congenital disease characterized by severe defects in nervous system development. It is caused by mutations in alpha-phosphomannomutase (of which there are two isozymes, alpha-PMM1 and alpha-PPM2). Here we report the x-ray crystal structures of human alpha-PMM1 in the open conformation, with and without the bound substrate, alpha-D-mannose 1-phosphate. Alpha-PMM1, like most haloalkanoic acid dehalogenase superfamily (HADSF) members, consists of two domains, the cap and core, which open to bind substrate and then close to provide a solvent-exclusive environment for catalysis. The substrate phosphate group is observed at a positively charged site of the cap domain, rather than at the core domain phosphoryl-transfer site defined by the Asp(19) nucleophile and Mg(2+) cofactor. This suggests that substrate binds first to the cap and then is swept into the active site upon cap closure. The orientation of the acid/base residue Asp(21) suggests that alpha-phosphomannomutase (alpha-PMM) uses a different method of protecting the aspartylphosphate from hydrolysis than the HADSF member beta-phosphoglucomutase. It is hypothesized that the electrostatic repulsion of positive charges at the interface of the cap and core domains stabilizes alpha-PMM1 in the open conformation and that the negatively charged substrate binds to the cap, thereby facilitating its closure over the core domain. The two isozymes, alpha-PMM1 and alpha-PMM2, are shown to have a conserved active-site structure and to display similar kinetic properties. Analysis of the known mutation sites in the context of the structures reveals the genotype-phenotype relationship underlying CDG-1a.
Silvaggi
Nicholas R
NR
Department of Physiology and Biophysics, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118, USA.
Zhang
Chunchun
C
Lu
Zhibing
Z
Dai
Jianying
J
Dunaway-Mariano
Debra
D
Allen
Karen N
KN
D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000737:chemistry; D002239:Carbohydrate Metabolism, Inborn Errors / Q000235:genetics* / Q000378:metabolism*; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray / Q000379:methods*; D006801:Humans; D006867:Hydrolases / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D017875:Phosphotransferases (Phosphomutases) / Q000737:chemistry*; D020033:Protein Isoforms
D020033:Protein Isoforms; D001224:Aspartic Acid; D006867:Hydrolases; C034507:2-haloacid dehalogenase; D017875:Phosphotransferases (Phosphomutases); C052799:phosphomannomutase; D008274:Magnesium