Crystal Structure of Human Taspase1, a Crucial Protease Regulating the Function of MLL  Javed A. Khan, Ben M. Dunn, Liang Tong  Structure  Volume 13, Issue 10, Pages 1443-1452 (October 2005) DOI: 10.1016/j.str.2005.07.006 Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 1 Sequence Alignment of Human (hs), Drosophila melanogaster (dm), and Arabidopsis thaliana (at) Taspase1 (Tas1) Also shown is the structure-based alignment with human lysosomal aspartylglucosaminidase (AGA). The secondary structure elements are labeled (S. S.). The catalytic Thr residue is shown in red, which is the N terminus of the β subunit. Residues shown in green are in the active site of Taspase1, whereas those shown in magenta are in the dimer interface of Taspase1 or AGA. Residues shown in uppercase in AGA are located within 3 Å of their equivalent residues in Taspase1, and residues shown in italic lowercase are disordered in the structure of Taspase1. Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 2 Structure of Taspase1 (A) Stereo diagram showing a schematic representation of the structure of activated Taspase1. The α subunit is shown in cyan, and the β subunit in yellow. The β strands and α helices are labeled, and the catalytic Thr234 residue is shown in green. The chloride ion is shown as a gray sphere. (B) Structure of the proenzyme of Taspase1. The β strands are shown in cyan, α helices in yellow, and connecting loops in magenta. Produced with Ribbons (Carson, 1987). Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 3 Structure of the Dimer of Taspase1 The α subunits are shown in cyan and magenta, and the β subunits in yellow and gray, respectively. Produced with Ribbons (Carson, 1987). Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 4 The Active Site of Taspase1 (A) Stereo diagram showing the active site of Taspase1, in an overlap between the activated enzyme (cyan and yellow for main chain of α and β subunits, respectively; green for side chain) and proenzyme (magenta for main chain, gray for side chain). Residues 232–233 of the proenzyme (D233A mutant) are shown as stick models. A water molecule is shown as a red sphere and labeled W. Produced with Ribbons (Carson, 1987). (B) Molecular surface of the active site region of activated Taspase1. Residues 232–233 of the proenzyme are shown in green, and residue 233 has been modeled as Asp. (C) Molecular surface of the active site region of the proenzyme of Taspase1. (B) and (C) produced with Grasp (Nicholls et al., 1991). Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 5 Structural Overlay of Taspase1 and AGA The α and β subunits of Taspase1 are shown in cyan and yellow, respectively, and the structure of AGA is shown in magenta. Arrowheads point to regions of differences between the two structures. Produced with Ribbons (Carson, 1987). Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 6 Kinetic Studies of Taspase1 (A) Reaction progress curves for the cleavage of the fluorogenic substrate by wild-type (WT) and mutant Taspase1. (B) Plot of initial reaction velocity of Taspase1 as a function of the concentration of the fluorogenic substrate. (C) Plot of initial reaction velocity of Taspase1 as a function of the concentration of chloride ions. The IC50 for the inhibition of Taspase1 activity by chloride ions is 26 mM. (D) Characterization of the effects of mutations in the active site region on the catalytic activity of Taspase1. The initial velocity was determined at two different substrate concentrations, 2 μM (in blue) and 10 μM (in red). The velocity for the wild-type enzyme (WT) is scaled to 100. Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 7 A Chloride Binding Site in the Active Site of Taspase1 The chloride ion is shown as a gray sphere, and its interactions with the enzyme are indicated with the thin gray lines. Produced with Ribbons (Carson, 1987). Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions

Figure 8 Mutation of Thr234 Blocks Autoprocessing but May Not Abolish Catalysis In trans (A) Overlay of the structures of the wild-type (in cyan) and T234A (in yellow) and T234S (in magenta) mutants in the active site region. (B) A gel showing the autoprocessing of the wild-type enzyme (WT) after expression and purification of the proenzyme in E. coli. In comparison, the T234S, T234A, T234C, D233A, and D233N mutants show essentially no autoprocessing. Structure 2005 13, 1443-1452DOI: (10.1016/j.str.2005.07.006) Copyright © 2005 Elsevier Ltd Terms and Conditions