title: Domain III of calpain is a ca2+-regulated phospholipid-binding domain.
abstract: The X-ray structure of m-calpain shows that domain III of the large subunit is structurally related to C2 domains, Ca2+-regulated lipid binding modules in many enzymes. To address whether this structural similarity entails functional analogy, we have characterized recombinant domain III from rat micro- and m-calpain and Drosophila CALPB. In a Ca2+ overlay assay domain III displays a large capacity for Ca2+ binding, commensurable with that of domain IV, the principal Ca2+-binding domain of calpains. The amount of Ca2+ bound to domain III increases 2- to 10-fold upon the addition of liposomes containing 20-40% di- and triphosphoinositides. Conversely, phospholipid-binding in spin-column size-exclusion chromatography is significantly promoted by Ca2+, in a manner similar to known C2 domains. These results suggest that domain III might be the primary lipid binding site of calpain and may play a decisive role in orchestrating Ca2+- and lipid activation of the enzyme.
authors.affiliation: Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, H-1518, Hungary. tompa@enzim.hu
authors.forename: P
authors.initials: P
authors.lastname: Tompa
authors.forename: Y
authors.initials: Y
authors.lastname: Emori
authors.forename: H
authors.initials: H
authors.lastname: Sorimachi
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.forename: P
authors.initials: P
authors.lastname: Friedrich
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002154:Calpain / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D004330:Drosophila / Q000235:genetics; D008081:Liposomes / Q000378:metabolism; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D008081:Liposomes; D010743:Phospholipids; D011994:Recombinant Proteins; D002154:Calpain; D002118:Calcium