Fig. 3 Organization of the active site of DHHC20. Organization of the active site of DHHC20. (A) Close-up of the Zn2+ binding region showing coordination of each Zn2+ ion by three cysteines and one histidine in a CCHC configuration. (B) Close-up of the DHHC enzyme active site showing the catalytic Cys156 pointing upward toward a hydrophobic groove. Also shown are the aspartic acid and the first histidine of the DHHC motif and the Thr241 of the TTXE motif. Hydrogen-bonding interactions are shown with dotted lines. Trp158, Phe171, and Phe174, which form the base of the acyl-binding cavity in Fig. 2D, are also shown in stick rendition. (C) Analysis of the enzymatic activity of selected mutants of the active site residues shown in (B). The coupled-enzyme assay was used, and Michaelis-Menten fits are shown. AHHC, DAHC, and F171A mutant curves all overlay with essentially no enzyme activity. Data are mean ± SEM of two independent measurements. Single-letter abbreviations for amino acid residues are as follows: A, Ala; C, Cys; D, Asp; E, Glu; F, Phe; G, Gly; H, His; I, Ile; K, Lys; L, Leu; M, Met; N, Asn; P, Pro; Q, Gln; R, Arg; S, Ser; T, Thr; V, Val; W, Trp; and Y, Tyr. Mitra S. Rana et al. Science 2018;359:eaao6326 Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works