GDP-mannose pyrophosphorylase A, B (GMPPA, B)

Abstract

GDP-mannose (GDP-Man) is the central activated sugar nucleotide for mannosylation and is essential for the biosynthesis of N-linked glycoproteins and glycosylphosphatidylinositol anchors (GPI-anchors) in eukaryotes as well as for the formation of bacterial capsular lipopolysaccharides. In addition, GDP-Man is well known to be one of the sources of GDP-fucose (GDP-Fuc), another sugar nucleotide critical for glycosylation in eukaryotes and microbial cells, and is one of the essential intermediates for the biosynthesis of vitamin C (l-ascorbic acid) in plants (Conklin et al. 1999b, 2006). GDP-mannose pyrophosphorylase (GMPP) enzyme, which is highly conserved from bacteria to human, catalyzes the reaction to form GDP-Man from mannose-1-phosphate (Man-1-P) and GDP in the cytosol. Following successful cloning of the gene encoding GMPP from baker’s yeast, Saccharomyces cerevisiae (Hashimoto et al. 1997), homologues of the gene have been cloned from a number of organisms and are categorized into two groups based on complex formation. In one group, which includes many animal, plant, fly, worm, and fission yeast homologues, GMPP forms a heterodimeric complex consisting of an α-subunit, GDP-Man pyrophosphorylase A (GMPPA), and a catalytic β-subunit, GDP-Man pyrophosphorylase B (GMPPB). In the other group, which includes protozoa, budding yeast, and bacteria, GMPP does not have the α-subunit. In yeast such as S. cerevisiae and Candida albicans, the deletion of structural gene coding GMPP is lethal because the lack of GDP-Man leads to the malformation of N-glycans, O-glycans, and GPI-anchors and, therefore, defects in the architecture and integrity of the cell wall (Warit et al. 2000). In contrast, the deletion of gene coding GMPP in the pathogenic protozoan, Leishmania mexicana, does not show lethal phenotype, but unable to infect macrophages or mice due to a defect in the formation of large amounts of mannose-containing glycoconjugates on the cell surface (Garami and Ilg 2001).