ICA512 (or IA-2) is a transmembrane protein-tyrosine phosphatase located in secretory granules of neuroendocrine cells. Initially, it was identified as one of the main antigens of autoimmune diabetes. Later, it was found that during insulin secretion, the cytoplasmic domain of ICA512 is cleaved and relocated to the nucleus, where it stimulates the transcription of the insulin gene. The role of the other parts of the receptor in insulin secretion is yet to be unveiled. The structures of the intracellular pseudocatalytic and mature extracellular domains are known, but the transmembrane domain and several intracellular and extracellular parts of the receptor are poorly characterized. Moreover the overall structure of the receptor remains to be established. We started to address this issue studying by X-ray crystallography the structure of the mature ectodomain of ICA512 (ME ICA512) and variants thereof. The variants and crystallization conditions were chosen with the purpose of exploring putative association interfaces, metal binding sites and all other structural details that might help, in subsequent works, to build a model of the entire receptor. Several structural features were clarified and three main different association modes of ME ICA512 were identified. The results provide essential pieces of information for the design of new experiments aimed to assess the structure in vivo.
References
[1]
Andersen JN, Jansen PG, Echwald SM, Mortensen OH, Fukada T, et al. (2004) A genomic perspective on protein tyrosine phosphatases: gene structure, pseudogenes, and genetic disease linkage. FASEB J 18: 8–30.
[2]
Brady-Kalnay SM, Tonks NK (1995) Protein tyrosine phosphatases as adhesion receptors. Curr Opin Cell Biol 7: 650–657.
[3]
Solimena M, Dirkx R Jr, Hermel JM, Pleasic-Williams S, Shapiro JA, et al. (1996) ICA 512, an autoantigen of type I diabetes, is an intrinsic membrane protein of neurosecretory granules. EMBO J 15: 2102–2114.
[4]
Lan MS, Wasserfall C, Maclaren NK, Notkins AL (1996) IA-2, a transmembrane protein of the protein tyrosine phosphatase family, is a major autoantigen in insulin-dependent diabetes mellitus. Proc Natl Acad Sci USA 93: 6367–6370.
[5]
Kubosaki A, Nakamura S, Notkins AL (2005) Dense core vesicle proteins IA-2 and IA-2beta: metabolic alterations in double knockout mice. Diabetes 54: S46–51.
[6]
Kubosaki A, Nakamura S, Clark A, Morris JF, Notkins AL (2006) Disruption of the transmembrane dense core vesicle proteins IA-2 and IA-2beta causes female infertility. Endocrinology 147: 811–815.
[7]
Suckale J, Solimena M (2010) The insulin secretory granule as a signaling hub. Trends Endocrinol Metab 21: 599–609.
[8]
Trajkovski M, Mziaut H, Altkruger A, Ouwendijk J, Knoch KP, et al. (2004) Nuclear translocation of an ICA512 cytosolic fragment couples granule exocytosis and insulin expression in β-cells. J Cell Biol 167: 1063–1074.
[9]
Schubert S, Knoch KP, Ouwendijk J, Mohammed S, Bodrov Y, et al. (2010) beta2-Syntrophin is a Cdk5 substrate that restrains the motility of insulin secretory granules. PloS one 5: e12929.
[10]
van der Wijk T, Overvoorde J, den Hertog J (2004) H2O2-induced intermolecular disulfide bond formation between receptor protein-tyrosine phosphatases. J Biol Chem 279: 44355–44361.
[11]
Bilwes AM, den Hertog J, Hunter T, Noel JP (1996) Structural basis for inhibition of receptor protein-tyrosine phosphatase-alpha by dimerization. Nature 382: 555–559.
[12]
van der Wijk T, Blanchetot C, Overvoorde J, den Hertog J (2003) Redox-regulated rotational coupling of receptor protein-tyrosine phosphatase alpha dimers. J Biol Chem 278: 13968–13974.
[13]
Chin CN, Sachs JN, Engelman DM (2005) Transmembrane homodimerization of receptor-like protein tyrosine phosphatases. FEBS Lett 579: 3855–3858.
[14]
Gross S, Blanchetot C, Schepens J, Albet S, Lammers R, et al. (2002) Multimerization of the protein-tyrosine phosphatase (PTP)-like insulin-dependent diabetes mellitus autoantigens IA-2 and IA-2beta with receptor PTPs (RPTPs). Inhibition of RPTPalpha enzymatic activity. J Biol Chem 277: 48139–48145.
[15]
Primo ME, Klinke S, Sica MP, Goldbaum FA, Jakoncic J, et al. (2008) Structure of the mature ectodomain of the human receptor-type protein-tyrosine phosphatase IA-2. J Biol Chem 283: 4674–4681.
[16]
Bork P, Patthy L (1995) The SEA module: a new extracellular domain associated with O-glycosylation. Protein Sci 4: 1421–1425.
[17]
Andersen JN, Mortensen OH, Peters GH, Drake PG, Iversen LF, et al. (2001) Structural and evolutionary relationships among protein tyrosine phosphatase domains. Mol Cell Biol 21: 7117–7136.
[18]
Primo ME, Sica MP, Risso VA, Poskus E, Ermácora MR (2006) Expression and physicochemical characterization of an extracellular segment of the receptor protein tyrosine phosphatase IA-2. Biochim Biophys Acta 1764: 174–181.
[19]
Otwinowski Z, Minor W (1997) Processing of X-ray Diffraction Data Collected in Oscillation Mode. Methods Enzymol 276: 307–326.
[20]
Emsley P, Cowtan K (2004) Coot: model-building tools for molecular graphics. Acta Crystallogr D Biol Crystallogr 60: 2126–2132.
[21]
Murshudov GN, Vagin AA, Dodson EJ (1997) Refinement of macromolecular structures by the maximum-likelihood method. Acta Crystallogr D Biol Crystallogr 53: 240–255.
[22]
Humphrey W, Dalke A, Schulten K (1996) Visual Molecular Dynamic. J Mol Graph 14: 33–38.
[23]
Van Der Spoel D, Lindahl E, Hess B, Groenhof G, Mark AE, et al. (2005) GROMACS: fast, flexible, and free. J Comput Chem 26: 1701–1718.
[24]
Feenstra KA, Hess B, Berendsen HJC (1999) Improving efficiency of large time-scale molecular dynamics simulations of hydrogen-rich systems. J Comput Chem 20: 786–798.
[25]
Hubbard TJ, Murzin AG, Brenner SE, Chothia C (1997) SCOP: a structural classification of proteins database. Nucleic Acids Res 25: 236–239.
[26]
Zhu J, Luo BH, Xiao T, Zhang C, Nishida N, et al. (2008) Structure of a Complete Integrin Ectodomain in a Physiologic Resting State and Activation and Deactivation by Applied Forces. Mol Cell 32: 849–861.
[27]
Lu C, Mi LZ, Grey MJ, Zhu J, Graef E, et al. (2010) Structural evidence for loose linkage between ligand binding and kinase activation in the epidermal growth factor receptor. Mol Cell Biol 30: 5432–5443.
[28]
André I, Strauss CEM, Kaplan DB, Bradley P, Baker D (2008) Emergence of symmetry in homooligomeric biological assemblies. Proc Natl Acad Sci USA 105: 16148–16152.
