Characterization of a Novel Family of Calmodulin-Binding Plasma Membrane Channel-Like Proteins

Abstract

Calcium (Ca²⁺) is a ubiquitous second messenger in all eukaryotes (reviewed by Clapham, 1995; Bush, 1995; McAinsh and Hetherington, 1998). Ca²⁺ signals are transduced primarily by Ca²⁺ modulated proteins such as calmodulin (CaM) (Van Eldik and Watterson, 1998). CaM has no catalytic activity of its own and its diverse functions are the result of its interactions with numerous downstream effectors such as protein kinases, phosphatases, ion channels, and cytoskeleton associated proteins (James et al., 1995). The role of CaM and CaM-related proteins in plants is being unraveled in recent years (Snedden and Fromm, 1998; Zielinski, 1998). It became apparent that in spite of the high similarity of CaM from plants with that in animals (close to 90% identity in amino acid sequence) the downstream targets of CaM in plants and animals are not all the same (Baum et al., 1996; Snedden and Fromm, 1998). In addition, plants possess a large repertoire of calmodulin-related proteins not present in other eukaryotes (Snedden and Fromm, 1998). Thus, plants use the Ca²⁺/CaM messenger system in unique ways to accommodate their physiological requirements.