Comparative modeling of the three-dimensional structure of the calmodulin-related TCH2 protein from arabidopsis

Abstract

Plants adapt to various stresses by developmental alterations that render them less easily damaged. Expression of the TCH2 gene of Arabidopsis is strongly induced by stimuli such as touch and wind. The gene product, TCH2, belongs to the calmodulin (CaM) family of proteins and contains four highly conserved Ca(2+)-binding EF-hands. We describe here the structure of TCH2 in the fully Ca(2+)-saturated form, constructed using comparative molecular modeling, based on the x-ray structure of paramecium CaM. Like known CaMs, the overall structure consists of two globular domains separated by a linker helix. However, the linker region has added flexibility due to the presence of 5 glycines within a span of 6 residues. In addition, TCH2 is enriched in Lys and Arg residues relative to other CaMs, suggesting a preference for targets which are more negatively charged. Finally, a pair of Cys residues in the C-terminal domain, Cys126 and Cys131, are sufficiently close in space to form a disulfide bridge. These predictions serve to direct future biochemical and structural studies with the overall aim of understanding the role of TCH2 in the cellular response of Arabidopsis to environmental stimuli.

CML24, Regulated in Expression by Diverse Stimuli, Encodes a Potential Ca2+ Sensor That Functions in Responses to Abscisic Acid, Daylength, and Ion Stress

“…Ca 21 binding by CaM and the resulting conformational change can be detected as a mobility shift in SDS-PAGE (Burgess et al, 1980 (Fig. 1A) and modeled tertiary structure (Khan et al, 1997), are consistent with the idea that CML24 may function as a Ca 21 sensor.…”

“…This family of 50 genes encodes proteins that share at least 16% amino acid identity with CaM, contain one or more EF hands, and have no other predicted functional domains (McCormack and Braam, 2003). Comparisons of primary and tertiary protein structure (Khan et al, 1997) have revealed several features that distinguish CML24 from CaMs and other CMLs; these features may be important for differences in target interaction, localization, and/or stability.…”

“…CML24 is a CaM-related protein that shares approximately 40% overall sequence identity with CaM (Khan et al, 1997;McCormack and Braam, 2003). Primary amino acid sequence analyses and modeling studies predict that CML24 has four functional EF hands for Ca 21 binding and that upon Ca 21 binding conformational changes likely result in the exposure of hydrophobic patches, enabling target interaction (Khan et al, 1997).…”

“…Primary amino acid sequence analyses and modeling studies predict that CML24 has four functional EF hands for Ca 21 binding and that upon Ca 21 binding conformational changes likely result in the exposure of hydrophobic patches, enabling target interaction (Khan et al, 1997). Sequence diversity from CaM suggests that CML24 target proteins would be distinct from those of CaM.…”

An inducible helix–Gly–Gly–helix motif in the N‐terminal domain of histone H1e: A CD and NMR study

“…Another example of structural flexibility associated with a Gly sequence is that of the calmodulin-related TCH2 protein from Arabidopsis. Its overall structure consists of two globular domains separated by a flexible linker region that contains a (Gly) 4 motif (Khan et al 1997). Figure 5 (B and C) shows a representation of the binding of the N-terminal domain to the DNA in chromatin.…”