Figure 5. Active centre of DEP–TAP complex structure.

The crystallographic structure (PDB code 1J00) [22] shows DEP covalently bound to Ser¹⁰, which indicates that Ser¹⁰ is acting as a nucleophilic attacker towards the ester bond of substrate. The broken lines denote possible hydrogen-bonding between atoms. Amide protons of Ser¹⁰ and Gly⁴⁴ could serve as hydrogen-bond donors for oxyanion. H^δ of Asn⁷³ could devote further constraint by hydrogen-bonding to stabilizing oxyanion structure. After activating Ser¹⁰, the HN^ϵ2 of His¹⁵⁷ may serve as a hydrogen-bond donor for the bound substrate in the transition state. The inset shows the superimposition of the region S⁴¹ISGDTSQ⁴⁸ of the two structures, native TAP (PDB code 1IVN, denoted by N) and TAP–DEP complex (PDB code 1J00, denoted by DEP). Ser⁴³ extends its side chain in a distinctly different direction in the two situations. The Figure was prepared using the ViewerLite (version 5.0) program.