The X-ray Crystal Structures of Human {alpha}-Phosphomannomutase 1 Reveal the Structural Basis of Congenital Disorder of Glycosylation Type 1a
Carbohydrate-deficient glycoprotein syndrome 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 D19 nucleophile and Mg{sup 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 D21 suggests that {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.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 914153
- Report Number(s):
- BNL-78721-2007-JA; JBCHA3; TRN: US200804%%556
- Journal Information:
- J. Biol. Chem., Vol. 281, Issue 21; ISSN 0021-9258
- Country of Publication:
- United States
- Language:
- English
Similar Records
Solution NMR of a 463-Residue Phosphohexomutase: Domain 4 Mobility, Substates, and Phosphoryl Transfer Defect
The X-ray Crystallographic Structure and Activity Analysis of a Pseudomonas-Specific Subfamily of the HAD Enzyme Superfamily Evidences a Novel Biochemical Function