InterPro domain: IPR024927

Acid phosphatase 5 (ACP5; EC 3.1.3.2) removes the mannose 6-phosphate recognition marker from lysosomal proteins. The exact site of dephosphorylation is not clear. Evidence suggests dephosphorylation may take place in a prelysosomal compartment as well as in the lysosome [ 1 ]. ACP5 belongs to the metallophosphatase (MPP) superfamily. MPPs are functionally diverse, but all share a conserved domain with an active site consisting of two metal ions (usually manganese, iron, or zinc) co-ordinated with octahedral geometry by a cage of histidine, aspartate, and asparagine residues [ 2 ].

This entry includes purple acid phosphatases (EC 3.1.3.2), which are metal dependent, binding two metal ions. Metal binding ligands and residues involved in resistance to tartrate inhibition are conserved [ 3 ].

Purple acid phosphatase 3, 4, 7, 8 and 17 are found in plants, bind zinc and iron, and the genes are predominantly transcribed in flowers [ 4 ]. Purple acid phosphatase 17 (PAP17) is induced in response to phosphate starvation, a condition occurring in phosphate-poor soils, and the plant hormone abscisic acid (ABA) and salt stress. Like mammalian acid phosphatase 5, PAP17 has peroxidation activity [ 5 ].

1. Acid phosphatase 5 is responsible for removing the mannose 6-phosphate recognition marker from lysosomal proteins. Proc. Natl. Acad. Sci. U.S.A. 105, 16590-5
2. Crystal structures of recombinant human purple Acid phosphatase with and without an inhibitory conformation of the repression loop. J. Mol. Biol. 351, 233-46
3. A type 5 acid phosphatase gene from Arabidopsis thaliana is induced by phosphate starvation and by some other types of phosphate mobilising/oxidative stress conditions. Plant J. 19, 579-89
4. Expression patterns of purple acid phosphatase genes in Arabidopsis organs and functional analysis of AtPAP23 predominantly transcribed in flower. Plant Mol. Biol. 59, 581-94