Leishmania major thialysine Nε-acetyltransferase:: Identification of amino acid residues crucial for substrate binding

Thialysine N-epsilon-acetyltransferases and spermidine/spermine N-acetyltransferases (SSAT) are closely related members of the GCN5-related N-acetyltransferase superfamily. Accordingly, a putative orthologue from the human protozoan parasite Leishmania major exhibits an almost equal similarity to human SSAT and thialysine N-acetyltransferase. Characterisation of the recombinantly expressed L. major protein indicated that it represents a thialysine N-acetyltransferase, preferring thialysine (S-aminoethyl-L-cysteine) and structurally related amino acids as acceptor molecules. The known thialysine N-epsilon-acetyltransferases contain five conserved amino acid residues that are replaced in SSAT sequences. Kinetic analyses of the respective recombinant mutant proteins suggest that Ser(82) and Thr(83) of L. major thialysine N-acetyltransferase are key residues for acceptor binding. In addition, the conserved Leu(130) is tentatively involved in specific interaction with the sulphur-containing side chain of thialysine. The presence of these three amino acid residues is suggested to be a means by which thialysine N-acetyltransferases can be distinguished from SSAT sequences. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.