SUMMARY PARAGRAPH for PCM1
UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) is the source of the first two GlcNAc moieties added during N-linked glycosylation of proteins and provides GlcNAc for synthesis of GPI anchors. In yeast, it is synthesized from fructose-6-phosphate (F6P) by the consecutive action of Gfa1p, Gna1p, Pcm1p, and Qri1p, although a different pathway (4, 5) is used in bacteria. UDP-GlcNAc is also the building block from which chitin, a linear polymer of beta-1,4-N-acetylglucosamine, is constructed. Chitin is a component of the cell wall deposited as a ring around the neck of the growing bud during cell division. Bud scars, the remnants of the chitinous primary septum seen on the surface of mother cells after division, are the primary repository of chitin (reviewed in 6).
PCM1 encodes phosphoacetylglucosamine mutase (EC 220.127.116.11) (1), which catalyzes the isomerization of GlcNAc-6-P to GlcNAc-1-P. While the reaction is reversible, GlcNAc-1-P is a substrate for Qri1p, which synthesizes UDP-GlcNAc. PCM1 is an essential gene. After sporulation of heterozygous diploids, spores lacking Pcm1p survive for only a few generations, forming undivided strings of four to five cells (1, 3) containing little or no chitin (3).
Interestingly, Pcm1p has enough nonspecific hexosephosphate mutase activity that overexpression of PCM1 complements a pgm1 pgm2 double mutant, which lacks the phosphoglucomutases that isomerize glucose-6-phosphate to glucose-1-phosphate (1, 7). The human homolog of PCM1 is called both AGM1 (phosphoacetylglucosamine mutase, as in yeast) and PGM3 (phosphoglucomutase) (8). Both human (OMIM) and Candida albicans AGM1 complement deletion of PCM1 (2).
Last updated: 2005-07-01