Leishmania major thialysine Nepsilon-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(epsilon)-acetyltransferase. Characterisation of the recombinantly expressed L. major protein indicated that it represents a thialysine N(epsilon)-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(epsilon)-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(epsilon)-acetyltransferases can be distinguished from SSAT sequences.