COMPARATIVE MODELING OF THE 3-DIMENSIONAL STRUCTURE OF THE CALMODULIN-RELATED TCH2 PROTEIN FROM ARABIDOPSIS

Plants adapt to various stresses by developmental alterations that ren der them less easily damaged. Expression of the TCH2 gene of Arabidops is is strongly induced by stimuli such as touch and wind. The gene pro duct, TCH2, belongs to the calmodulin (CaM) family of proteins and con tains four highly conserved Ca2+-binding EF-hands. We describe here th e structure of TCH2 in the fully Ca2+-saturated form, constructed usin g comparative molecular modeling, based on the x-ray structure of para mecium CaM. Like known CaMs, the overall structure consists of two glo bular 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 r elative to other CaMs, suggesting a preference for targets which are m ore negatively charged. Finally, a pair of Cys residues in the C-termi nal domain, Cys126 and Cys131, are sufficiently close in space to form a disulfide bridge. These predictions serve to direct future biochemi cal and structural studies with the overall aim of understanding the r ole of TCH2 in the cellular response of Arabidopsis to environmental s timuli. Proteins 27:144-153 (C) 1997 Wiley-Liss, Inc.