title: Crystal structure of human Taspase1, a crucial protease regulating the function of MLL.
abstract: Taspase1 catalyzes the proteolytic processing of the mixed lineage leukemia (MLL) nuclear protein, which is required for maintaining Hox gene expression patterns. Chromosomal translocations of the MLL gene are associated with leukemia in infants. Taspase1, a threonine aspartase, is a member of the type 2 asparaginase family, but is the only protease in this family. We report here the crystal structures of human activated Taspase1 and its proenzyme, as well as the characterization of the effects of mutations in the active site region using a newly developed fluorogenic assay. The structure of Taspase1 has significant differences from other asparaginases, especially near the active site. Mutation of the catalytic nucleophile, Thr234, abolishes autocatalytic processing in cis but does not completely block proteolysis in trans. The structure unexpectedly showed the binding of a chloride ion in the active site, and our kinetic studies confirm that chlorides ions are inhibitors of this enzyme at physiologically relevant concentrations.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
authors.forename: Javed A
authors.initials: JA
authors.lastname: Khan
authors.forename: Ben M
authors.initials: BM
authors.lastname: Dunn
authors.forename: Liang
authors.initials: L
authors.lastname: Tong
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D002712:Chlorides / Q000378:metabolism / Q000494:pharmacology; D018360:Crystallography, X-Ray; D019281:Dimerization; D010450:Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics; D005456:Fluorescent Dyes; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D051788:Myeloid-Lymphoid Leukemia Protein / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry
chemical_list: D002712:Chlorides; D004792:Enzyme Precursors; D005456:Fluorescent Dyes; C497422:KMT2A protein, human; D021122:Protein Subunits; D014867:Water; D051788:Myeloid-Lymphoid Leukemia Protein; D011495:Histone-Lysine N-Methyltransferase; D010450:Endopeptidases; D010447:Peptide Hydrolases; C480823:taspase1, human