title: Apoptosis-linked gene product ALG-2 is a new member of the calpain small subunit subfamily of Ca2+-binding proteins.
abstract: ALG-2 is a newly discovered Ca2+-binding protein which has been demonstrated to be directly linked to apoptosis. Structurally, ALG-2 is expressed as a single polypeptide chain corresponding to a 22 kDa protein containing five putative EF-hand Ca2+-binding sites. In this work, we have developed an efficient expression and purification scheme for recombinant ALG-2. Utilizing this protocol, we can routinely obtain purified recombinant protein with a yield of approximately 100 mg per liter of bacterial cell cultures. Gel filtration and chemical cross-linking experiments have shown that Ca2+-free ALG-2 forms a weak homodimer in solution. Biochemical and spectroscopic studies of truncated and point mutants of ALG-2 demonstrated that the fifth EF-hand Ca2+-binding motif is likely to participate in the formation of the dimer complex. Experimentally, both the amino- and carboxyl-terminal truncated mutants of ALG-2 have shown their ability to retain the structural, as well as, Ca2+-binding integrity when individually expressed in bacteria. In this respect, the N-terminal domain encompasses the first two EF-hands, and the C-terminal domain contains the remaining three EF-hands. Combining mutagenesis and spectroscopic studies, we showed that ALG-2 possesses two strong Ca2+-binding sites. Employing fluorescence spectroscopy and circular dichroism, we showed that the binding of Ca2+ to ALG-2 induced significant conformational changes in both the N-terminal and C-terminal domains of the protein. Furthermore, our studies demonstrated that Ca2+ binding to both strong Ca2+-binding sites of ALG-2 is required for ion-induced aggregation of the protein. We also report here the expression, purification, and partial characterization of a Ca2+-binding-deficient ALG-2 mutant (Glu47Ala/Glu114Ala). In light of its much decreased affinity for Ca2+, this mutant could prove to be instrumental in elucidating the Ca2+-mediated function of ALG-2 within the context of its cellular environment.
authors.affiliation: Department of Biochemistry, The Hong Kong University of Science and Technology, Kowloon.
authors.forename: K W
authors.initials: KW
authors.lastname: Lo
authors.forename: Q
authors.initials: Q
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D051017:Apoptosis Regulatory Proteins; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D002154:Calpain / Q000737:chemistry* / Q000235:genetics; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D051379:Mice; D008958:Models, Molecular; D005810:Multigene Family; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017354:Point Mutation; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification; D017386:Sequence Homology, Amino Acid; D012996:Solutions
chemical_list: D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins; C490815:Pdcd6 protein, mouse; D010446:Peptide Fragments; D011994:Recombinant Proteins; D012996:Solutions; D002154:Calpain; D002118:Calcium