title: The SANT2 domain of the murine tumor cell DnaJ-like protein 1 human homologue interacts with alpha1-antichymotrypsin and kinetically interferes with its serpin inhibitory activity.
abstract: The murine tumor cell DnaJ-like protein 1 or MTJ1/ERdj1 is a membrane J-domain protein enriched in microsomal and nuclear fractions. We previously showed that its lumenal J-domain stimulates the ATPase activity of the molecular chaperone BiP/GRP78 (Chevalier, M., Rhee, H., Elguindi, E. C., and Blond, S. Y. (2000) J. Biol. Chem. 275, 19620-19627). MTJ1/ERdj1 also contains a large carboxyl-terminal cytosolic extension composed of two tryptophan-mediated repeats or SANT domains for which the function(s) is unknown. Here we describe the cloning of the human homologue HTJ1 and its interaction with alpha(1)-antichymotrypsin (ACT), a member of the serine proteinase inhibitor (serpin) family. The interaction was initially identified in a two-hybrid screening and further confirmed in vitro by dot blots, native electrophoresis, and fluorescence studies. The second SANT domain of HTJ1 (SANT2) was found to be sufficient for binding to ACT, both in yeast and in vitro. Single tryptophan-alanine substitutions at two strictly conserved residues significantly (Trp-497) or totally (Trp-520) abolished the interaction with ACT. SANT2 binds to human ACT with an intrinsic affinity equal to 0.5 nm. Preincubation of ACT with nearly stoichiometric concentrations of SANT2 wild-type but not SANT2: W520A results in an apparent loss of ACT inhibitory activity toward chymotrypsin. Kinetic analysis indicates that the formation of the covalent inhibitory complex ACT-chymotrypsin is significantly delayed in the presence of SANT2 with no change on the catalytic efficiency of the enzyme. This work demonstrates for the first time that the SANT2 domain of MTJ1/HTJ1/ERdj1 mediates stable and high affinity protein-protein interactions.
authors.affiliation: Center for Pharmaceutical Biotechnology, College of Pharmacy, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois, Chicago, Illinois 60607-7173, USA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Kroczynska
authors.forename: Christina M
authors.initials: CM
authors.lastname: Evangelista
authors.forename: Shalaka S
authors.initials: SS
authors.lastname: Samant
authors.forename: Ebrahim C
authors.initials: EC
authors.lastname: Elguindi
authors.forename: Sylvie Y
authors.initials: SY
authors.lastname: Blond
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D000091342:Endoplasmic Reticulum Chaperone BiP; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000378:metabolism*; D000514:alpha 1-Antichymotrypsin / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D017931:DNA Primers; D018076:DNA, Complementary; C485368:DNAJC1 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; D050956:HSP40 Heat-Shock Proteins; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D008565:Membrane Proteins; D015843:Serpins; D000514:alpha 1-Antichymotrypsin