CRYSTAL STRUCTURE OF TYROSINE AMINOTRANSFERASE FROM TRYPANOSOMA CRUZI

Blankenfeldt, W.¹, Montemartini, M² , Hunter, G. R.², Kalisz, H.¹; Nowicki, C.¹ &. Hecht, H.-J.¹

GBF, Gesellschaft für Biotechnologische Forschung, Mascheroder Weg 1, 38124 Braunschweig, Germany e-mail: hjh@gbf.de

Instítuto de Química y Fisicoquímica Bíologicas (IQUIFIB), Facultad de Farmacia Bioquimica, Universidad de Buenos Aires, Jumim 956,1113 Buenos Aires, Argentina

Tyrosine aminotransferase (TAT) is the most abundant protein in trypanosma cruzi, the causative agent of American trypanosomiasis (Chagas disease). The protein is a 90 kDa homodimer and catalyzes the transfer of the amino group from tyrosine to a-oxoacids like a- oxoglutarate or pyruvate in a pyridoxal phosphate (vitamin B6) dependent manner. Besides tyrosine it also tolerates other amino acids, e.g. alanine or aspartate. Its abundancy makes it an interesting drug target in the above mentioned disease[1].

TAT crystallizes in the monoclinic space group P2₁ with lattice constants a = 60.2, b =102.3, c = 78.1 Å and b =110.2^o, having one dimer per asymmetric unit. Diffraction data have been collected at the DESY beamline BW6 under cryogenic conditions. Crystals diffract to 2.3 Å resolution and a self rotation search reveals a clear peak for the dimer axis[2].

Initial phases could be obtained by molecular replacement using the substrate bound conforma- tion of aspartate aminotransferase from E.coli (PDB access code 1art)[3] with which TAT shows less than 20% sequence identity. Refinement and structure of TAT will be discussed.

[1] Montemartini, M.; Santome, J. A.; Cazzulo, J. J. & Nowicki, C.: Biochem. J. 292, 901-6 ( 1993)
[2] Nowicki, C.; Montemartini, M.; Hunter, G. R.; Blankenfeldt, W.; Kalisz, H. M. & Hecht, H.-J. Acta Cryst. D54,105-7 ( 1998)
[3] Okamoto, A.; Higuchi, T.; Hirotsu, K.; Kuramitsu, S. & Kagamiyama, H.: J.Biochem. 116, 95-107 ( 1994)