THE 3-DIMENSIONAL STRUCTURE OF N-ACETYLNEURAMINATE LYASE FROM ESCHERICHIA-COLI

Background: N-acetylneuraminate lyase catalyzes the cleavage of N-acet ylneuraminic acid (sialic acid) to form pyruvate and N-acetyl-D-mannos amine. The enzyme plays an important role in the regulation of sialic acid metabolism in bacteria. The reverse reaction can be exploited for die synthesis of sialic acid and some of its derivatives. Results: Th e structure of the enzyme from Escherichia coli has been determined to 2.2angstrom resolution by X-ray crystallography. The enzyme is shown to be a tetramer, in which each subunit consists of an alpha/beta-barr el domain followed by a carboxy-terminal extension of three alpha-heli ces. Conclusions: The active site of the enzyme is tentatively identif ied as a pocket at the carboxy-terminal end of the eight-stranded beta -barrel. Lys165 lies within this pocket and is probably the reactive r esidue which forms a Schiff base intermediate with the substrate. The sequence of N-acetylneuraminate lyase has similarities to those of dih ydrodipicolinate synthase and MosA (an enzyme implicated in rhizopine synthesis) suggesting that these last two enzymes share a similar stru cture to N-acetylneuraminate lyase.