Download MendeleyThe Crystal Structure of the Sorcin Calcium Binding Domain Provides a Model of Ca(2+)-Dependent Processes in the Full-Length Protein
Ilari, A., Johnson, K., Nastopoulos, V., Verzili, D., Zamparelli, C., Colotti, G., Tsernoglou, D., Chiancone, E.(2002) J Mol Biol 317: 447
- PubMed: 11922676
- DOI: https://doi.org/10.1006/jmbi.2002.5417
- Primary Citation of Related Structures:
1GJY - PubMed Abstract:
Sorcin is a 21.6 kDa calcium binding protein, expressed in a number of mammalian tissues that belongs to the small, recently identified penta-EF-hand (PEF) family. Like all members of this family, sorcin undergoes a Ca2+-dependent translocation from cytosol to membranes where it binds to target proteins. For sorcin, the targets differ in different tissues, indicating that it takes part in a number of Ca2+-regulated processes. The sorcin monomer is organized in two domains like in all PEF proteins: a flexible, hydrophobic, glycine-rich N-terminal region and a calcium binding C-terminal domain. In vitro, the PEF proteins are dimeric in their Ca2+-free form, but have a marked tendency to precipitate when bound to calcium. Stabilization of the dimeric structure is achieved by pairing of the uneven EF-hand, EF5. Sorcin can also form tetramers at acid pH. The sorcin calcium binding domain (SCBD, residues 33-198) expressed in Escherichia coli was crystallized in the Ca2+-free form. The structure was solved by molecular replacement and was refined to 2.2 A with a crystallographic R-factor of 22.4 %. Interestingly, the asymmetric unit contains two dimers. The structure of the SCBD leads to a model that explains the solution properties and describes the Ca2+-induced conformational changes. Phosphorylation studies show that the N-terminal domain hinders phosphorylation of SCBD, i.e. the rate of phosphorylation increased twofold in the absence of the N-terminal region. In addition, previous fluorescence studies indicated that hydrophobic residues are exposed to solvent upon Ca2+ binding to full-length sorcin. The model accounts for these data by proposing that Ca2+ binding weakens the interactions between the two domains and leads to their reorientation, which exposes hydrophobic regions facilitating the Ca2+-dependent binding to target proteins at or near membranes.
Organizational Affiliation:
CNR, Centro Studio sulla Biologia Molecolare and Dipartimento di Scienze Biochimiche, Università La Sapienza, P.le Aldo Moro 5, Roma, 00185, Italy.
