InterPro: IPR018050 Phosphomannose isomerase, type I, conserved site

Phosphomannose isomerase (PMI) [1, 2] is the enzyme that catalyzes the interconversion of mannose-6-phosphate and fructose-6-phosphate. In eukaryotes, it is involved in the synthesis of GDP-mannose which is a constituent of N- and O-linked glycans as well as GPI anchors. In prokaryotes, it is involved in a variety of pathways including capsular polysaccharide biosynthesis and D-mannose metabolism.

Three classes of PMI have been defined on the basis of sequence similarities [1]. The first class comprises all known eukaryotic PMI as well as the enzyme encoded by the manA gene in enterobacteria such as Escherichia coli. Class I PMI's are proteins of about 42 to 50 kDa which bind a zinc ion essential for their activity.

Two conserved regions define class I PMI. The first one is located in the N-terminal section of the proteins, the second in the C-terminal half. Both patterns contain a residue involved in the binding of the zinc ion [3].