4 hydroxymethyl phenylacetic acid

Two additional complexes were obtained from soaks. One including Tris and DMSO (PDB code 6MKM) was obtained from a soak that also included a reported arylstibonic acid inhibitor, compound 13755, from the NCI Diversity Set. In this case, the crystals were grown as described above and then soaked in 100 mM Tris, pH 7.5, 200 mM NaCl, 1 mM 13755 (dissolved in DMSO resulting in a final concentration of 4% DMSO), and 20% PEG 3350. Crystals were cryocooled in 100 mM Tris-Cl, pH 7.5, 200 mM NaCl, 20% PEG 3350, 1 mM 13755, 4% DMSO, and 20% ethylene glycol. The second complex included Mg²⁺ and DMSO (PDB code 6MKK), obtained from a soak including 20 mM 4-hydroxymethylphenylacetic acid (Sigma-Aldrich) along with 1 mM MgCl₂. Crystals were cryocooled in 100 mM MES, pH 6.0, 200 mM NaCl, 22% PEG4000, 20–22% ethylene glycol, 20 mM 4-(hydroxymethyl)-phenylacetic acid, and 4% DMSO. In each of these complexes, the inhibitor was not evident in the difference electron density map but DMSO was bound to the abasic sugar site with either Mg²⁺ or Tris in the metal binding site.