in C c s

and polarity. Modeling of a substrate-bound state finding made PGA the founding member of the N-terminal nucle-ophile hydrolase (Ntn-hydrolase) superfamily (Brannigan et al.,acid side chain of isopenicillin N (IPN) for a coenzyme A-acti-vated phenylacetic acid side chain, resulting in the formation of penicillin G (Figure 1). AT can also exchange other acyl side cam.ac.uk/scop/; Andreeva et al., 2004; Murzin et al., 1995). However, AT does not show obvious amino acid sequence homology to these or other enzymes, and therefore we initiatedchains, accepting a wide range of acyl-CoA derivatives, hydro-phobic as well as hydrophilic ones. It even accepts various non-CoA thioesters as substrate. This property makes AT an crystal structure determinations of precursor and mature AT to obtain deeper insights into its structure and functioning. AT appears to be a small representative of the Ntn-hydrolaseindicates the residues important for catalysis. Comparison of the proposed autoproteolytic and substrate hydrolysis mechanisms shows that in both events the same catalytic residues are used, but that they perform different roles in catalysis