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

Thialysine Nε-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 Nε-acetyltransferase. Characterisation of the recombinantly expressed L. major protein indicated that it represents a thialysine Nε-acetyltransferase, preferring thialysine (S-aminoethyl-l-cysteine) and structurally related amino acids as acceptor molecules. The known thialysine Nε-acetyltransferases contain five conserved amino acid residues that are replaced in SSAT sequences. Kinetic analyses of the respective recombinant mutant proteins suggest that Ser82 and Thr83 of L. major thialysine Nε-acetyltransferase are key residues for acceptor binding. In addition, the conserved Leu130 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 Nε-acetyltransferases can be distinguished from SSAT sequences.