InterPro: IPR006375 Mannose-1-phosphate guanylyltransferase/mannose-6-phosphate isomerase

This enzyme is known to be bifunctional, as both mannose-6-phosphate isomerase (EC:5.3.1.8) (PMI) and mannose-1-phosphate guanylyltransferase (EC:2.7.7.22) in Pseudomonas aeruginosa, Xanthomonas campestris, and Acetobacter xylinus. The literature on the enzyme from Escherichia coli attributes mannose-6-phosphate isomerase activity to an adjacent gene, but the present sequence has not been shown to lack the activity. The PMI domain lies at the C-terminal.

Mannose-6-phosphate isomerase or phosphomannose isomerase (PMI) is the enzyme that catalyses the interconversion of mannose-6-phosphate and fructose-6-phosphate. In eukaryotes PMI is involved in the synthesis of GDP-mannose, a constituent of N- and O-linked glycans and GPI anchors and in prokaryotes it participates in a variety of pathways, including capsular polysaccharide biosynthesis and D-mannose metabolism. PMI's belong to the cupin superfamily whose functions range from isomerase and epimerase activities involved in the modification of cell wall carbohydrates in bacteria and plants, to non-enzymatic storage proteins in plant seeds, and transcription factors linked to congenital baldness in mammals [1]. Three classes of PMI have been defined [2].