<p>Deoxythymidine diphosphate (dTDP)-4-keto-6-deoxy-d-hexulose 3, 5-epimerase (RmlC, <db_xref db="EC" dbkey="5.1.3.13"/>) is involved in the biosynthesis of dTDP-l-rhamnose, which is an essential component of the bacterial cell wall, converting dTDP-4-keto-6-deoxy-D-glucose to dTDP-4-keto-L-rhamnose.</p> <p>The crystal structure of RmlC from <taxon tax_id="187420">Methanobacterium thermoautotrophicum</taxon> was determined in the presence and absence of a substrate analogue. RmlC is a homodimer comprising a central jelly roll motif, which extends in two directions into longer beta-sheets. Binding of dTDP is stabilised by ionic interactions to the phosphate group and by a combination of ionic and hydrophobic interactions with the base. The active site, which is located in the centre of the jelly roll, is formed by residues that are conserved in all known RmlC sequence homologues. The active site is lined with a number of charged residues and a number of residues with hydrogen-bonding potentials, which together comprise a potential network for substrate binding and catalysis. The active site is also lined with aromatic residueswhich provide favorable environments for the base moiety of dTDP and potentially for the sugar moiety of the substrate [<cite idref="PUB00007928"/>].</p>