Sequential Calcium Binding to the Regulatory Domain of Calcium Vector Protein Reveals Functional Asymmetry and a Novel Mode of Structural Rearrangement

Autor: Sibyl Baladi, Isabelle Théret, Hiroshi Sakamoto, Jos A. Cox, Constantin T. Craescu
Rok vydání: 2000
Předmět:
Zdroj: Biochemistry. 39:7920-7926
ISSN: 1520-4995
0006-2960
DOI: 10.1021/bi000360z
Popis: Calcium vector protein (CaVP) from amphioxus is a two-domain, calcium-binding protein (18.3 kDa) of the calmodulin superfamily. Only two of the four EF-hand motifs (sites III and IV) have a significant binding affinity for calcium ions. We determined the solution structure of the domain containing these active sites (C-CaVP: W81-S161), in the Ca(2+)-saturated state, using NMR spectroscopy and restrained molecular dynamics. The tertiary structure is similar to other Ca(2+)-binding domains containing a pair of EF-hand motifs. The apo state has spectroscopic and thermodynamic characteristics of a molten globule, with conserved secondary structure but highly fluctuating tertiary organization. Titration of C-CaVP with Ca(2+) revealed a stepwise ion binding, with a stable equilibrium intermediate in which only site III binds a calcium ion. Despite a highly fluctuating structure of the free site IV, the calcium-bound site III has a persistent structure, with similar secondary elements but different interhelix angle and hydrophobic packing relative to the fully calcium-saturated state.
Databáze: OpenAIRE
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