Phosphatase Subfamily Auxilin

Phosphatase Classification: Superfamily CC1: Family PTEN: Subfamily Auxilin

Auxillins are pseudophosphatases and kinases that bind phospholipids and are involved in clathrin-coated vesicle function. Human forms are associated with Parkinson's disease.

Evolution

Auxilins are metazoan-specific, and lost from nematodes. Human has two members: auxilin and DNAJC6, which emerged by gene duplication in jawed vertebrates. The DNAJ domain appears to be much older and has orthologs in Arabidopsis (JAC1) and yeast (Swa2) that are also involved in clathrin uncoating, but lack phosphatase and kinase domains.

Domain Structure

Most auxillins are 1000-1500 AA long, with an N-terminal GAK kinase domain, a PTEN-like phosphatase domain in the middle, and a DnaJ domain at the very C-terminus. One of the two human homologs, DNAJC6/Auxillin-1 has lost the kinase domain.

Functions

Human GAK is known as Cyclin G-Associated Kinase, and associated with Cyclin G and CDK5 [1]. Both GAK and DNAJC6 are genetically implicated in Parkinson's disease and GAK physically associates with the Parkinson's kinase, LRRK2. Human DNAJC6 is only expressed in neuronal tissues, but GAK is widespread, and generally expressed higher in non-neuronal tissue. GAK and DNAJC6 bind clathrin heavy chain and are found in and required for the function of clathrin-associated vesicles, particularly by interacting with Hsc70 in uncoating of the vesicles [2]. GAK also binds AP1 and is required for endosomal sorting [3]. GAK can also localize to the nucleus and is required in a clathrin-dependent manner for mitosis [4].

Little is known about the phosphatase or kinase activities of auxilins, though one report shows that GAK phosphorylates and activates the PP2A complex [5]. The phosphatase domains of both are predicted to be inactive (HCx5R changed to HCx5A in both), and both GAK and DNAJC6 phosphatase domains have been shown to bind phospholipids, which are also involved in clathrin-coated vesicles [6, 7].

References

1. Kanaoka Y, Kimura SH, Okazaki I, Ikeda M, and Nojima H. GAK: a cyclin G associated kinase contains a tensin/auxilin-like domain. FEBS Lett. 1997 Jan 27;402(1):73-80. DOI:10.1016/s0014-5793(96)01484-6 |
2. Scheele U, Kalthoff C, and Ungewickell E. Multiple interactions of auxilin 1 with clathrin and the AP-2 adaptor complex. J Biol Chem. 2001 Sep 28;276(39):36131-8. DOI:10.1074/jbc.M106511200 |
3. Kametaka S, Moriyama K, Burgos PV, Eisenberg E, Greene LE, Mattera R, and Bonifacino JS. Canonical interaction of cyclin G associated kinase with adaptor protein 1 regulates lysosomal enzyme sorting. Mol Biol Cell. 2007 Aug;18(8):2991-3001. DOI:10.1091/mbc.e06-12-1162 |
4. Shimizu H, Nagamori I, Yabuta N, and Nojima H. GAK, a regulator of clathrin-mediated membrane traffic, also controls centrosome integrity and chromosome congression. J Cell Sci. 2009 Sep 1;122(Pt 17):3145-52. DOI:10.1242/jcs.052795 |
5. Naito Y, Shimizu H, Kasama T, Sato J, Tabara H, Okamoto A, Yabuta N, and Nojima H. Cyclin G-associated kinase regulates protein phosphatase 2A by phosphorylation of its B'γ subunit. Cell Cycle. 2012 Feb 1;11(3):604-16. DOI:10.4161/cc.11.3.19114 |
6. Lee DW, Wu X, Eisenberg E, and Greene LE. Recruitment dynamics of GAK and auxilin to clathrin-coated pits during endocytosis. J Cell Sci. 2006 Sep 1;119(Pt 17):3502-12. DOI:10.1242/jcs.03092 |
7. Kalli AC, Morgan G, and Sansom MS. Interactions of the auxilin-1 PTEN-like domain with model membranes result in nanoclustering of phosphatidyl inositol phosphates. Biophys J. 2013 Jul 2;105(1):137-45. DOI:10.1016/j.bpj.2013.05.012 |