The second of these, PriA (Figure ) from Mycobacterium tuberculosis (MtPriA), is also a TIM-barrel fold protein, and is a promiscuous catalyst of the Amadori rearrangements leading to the isomerization of substrates ProFAR and PRA by this enzyme. Our focus here is on the first step of this isomerization process, i.e. the ring-opening of substrate ProFAR (the first step of the mechanism shown in Figure ), following our prior work . Similarly to TPI, PriA also has a number of long loops decorating the active site, the conformational distribution of which is important for determining selectivity and activity . As discussed in detail elsewhere , one of these loops, loop 5, alternates between a knot-like "pro-ProFAR" and a β-hairpin "pro-PRA" conformation of the loop, depending on which substrate is being catalyzed. Here, we are starting from a structure of loop 5 in a pro-ProFAR conformation, as described in the Methodology section.