FIGURE 10.

Conserved essential Tpt1 amino acids colocalize at the putative active site. The tertiary structure of Aeropyrum pernix Tpt1 (pdb 1WFX) is depicted as a cartoon trace with cyan α helices and magenta β strands. The amino (N) and carboxl (C) termini of the protein are indicated. The C-terminal lobe is implicated in NAD⁺ binding on the basis of its homolog to the NAD⁺-binding module of Diphtheria toxin (pdb 1TOX). The four conserved amino acid side chains that are essential for the activity of SceTpt1, EcoKptA, and RslTpt1 are rendered as stick models with beige carbons and numbered according to their position in RslTpt1. Two chloride anions modeled in the ApeTpt1 structure are depicted as yellow spheres.