SUMMARY PARAGRAPH for PMI40
PMI40 encodes phosphomannose isomerase (EC 18.104.22.168), which catalyzes the isomerization between mannose-6-phosphate (M6P) and fructose-6-phosphate; M6P is a substrate for Sec53p and is used as a source of mannose for N-linked and O-linked glycosylation of proteins and GPI anchoring. Deletion or heat-inactivation of Pmi40p results in mannose auxotrophy, clumping, abnormal morphology, and defective secretion and cell-surface presentation of glycoproteins (2); unlike sec53, the pmi40 phenotype is suppressed if the growth medium is supplemented with mannose, presumably since mannose is imported into the cell as M6P, bypassing the need for PMI40 (1). Pmi40p is a zinc-dependent metalloenzyme; zinc, cadmium, and mercury are competitive inhibitors (3).
Mutations in the human homolog, PMI1 (OMIM), cause the congenital disorder of glycosylation CDG-Ib (OMIM). The human (4), Candida albicans (5), and Hansenula polymorpha (6) homologs all complement the pmi40 mutation. Deletion of the homolog MAN1 disrupts the pathogenicity of Cryptococcus neoformans (7).
Last updated: 2005-07-01