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Backbone dynamics of the regulatory domain of calcium vector protein, studied by 15 N relaxation at four fields, reveals unique mobility characteristics of the intermotif linker
Author(s) -
Théret Isabelle,
Cox Jos A.,
Mispelter Joel,
Craescu Constantin T.
Publication year - 2001
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.190101
Subject(s) - linker , chemistry , crystallography , ef hand , relaxation (psychology) , amide , microsecond , calcium , stereochemistry , calcium binding protein , physics , organic chemistry , computer science , operating system , psychology , social psychology , astronomy
CaVP is a calcium‐binding protein from amphioxus. It has a modular composition with two domains, but only the two EF‐hand motifs localized in the C‐terminal domain are functional. We recently determined the solution structure of this regulatory half (C‐CaVP) in the Ca 2+ ‐saturated form and characterized the stepwise ion binding. This paper reports the 15 N nuclear relaxation rates of the Ca 2+ ‐saturated C‐CaVP, measured at four different NMR fields (9.39, 11.74, 14.1, and 18.7 T), which were used to map the spectral density function for the majority of the amide H N ‐N vectors. Fitting the spectral density values at eight frequencies by a model‐free approach, we obtained the microdynamic parameters characterizing the global and internal movements of the polypeptide backbone. The two EF‐hand motifs, including the ion binding loops, behave like compact structural units with restricted mobility as reflected in the quite uniform order parameter and short internal correlation time (< 20 nsec). Comparative analysis of the two Ca 2+ binding sites shows that site III, having a larger affinity for the metal ion, is generally more rigid, and the amide vector in the second residue of each loop is significantly less restricted. The linker fragment is animated simultaneously by a larger amplitude fast motion and a slow conformational exchange on a microsecond to millisecond time scale. The backbone dynamics of C‐CaVP characterized here is discussed in relation with other well‐characterized Ca 2+ ‐binding proteins.