Class III PI 3-kinase

Class III PI 3-kinase is a subgroup of the enzyme family, phosphoinositide 3-kinase that share a common protein domain structure, substrate specificity and method of activation.

There is only one known class III PI 3-kinase, Vps34, it is also the only PI 3-kinase expressed in all eukaryotic cells. In humans it is encoded by the PIK3C3 gene. In human cells Vps34 associates with a regulatory subunit, p150.

Substrate specificity
Vps34 is more accurately described as a phosphatylinositol 3-kinase. In vivo Vps34 can only phosphorylate Phosphatidylinositol to form phosphatidylinositol (3)-phosphate (PtdIns(3)P).

Functions
Vps34 was first identified in a Saccharomyces cerevisiae (budding yeast) screen for proteins involved vesicle-mediated vacuolar protein sorting (hence Vps). A number of proteins containing a phosphoinositide binding domain specific for PtdIns(3)P have been identified which function in cellular protein trafficking.