INTERACTION OF ARABIDOPSIS KINESIN-LIKE CALMODULIN-BINDING PROTEIN WITH TUBULIN SUBUNITS - MODULATION BY CA2-CALMODULIN()

Kinesin-like calmodulin-binding protein (KCBP) is a recently identifie d novel kinesin-like protein that appears to be unique to and ubiquito us in plants. KCBP is distinct from all other known KLPs in having a c almodulin-binding domain adjacent to its motor domain. We have used di fferent regions of KCBP to study its interaction with tubulin subunits and the regulation of this interaction by Ca2+-calmodulin. The result s show that the carboxyterminal part of the KCBP, with or without calm odulin-binding domain, binds to tubulin subunits and this binding is s ensitive to nucleotides. In the presence of Ca2+-calmodulin the motor with calmodulin-binding domain does not bind to tubulin. This Ca2+-cal modulin modulation is abolished in the presence of antibodies specific to the calmodulin-binding domain of KCBP. Similar binding studies wit h the carboxy-terminal part of KCBP lacking the calmodulin-binding dom ain show no effect of Ca2+-calmodulin. These results indicate that Ca2 +-calmodulin modulates the interaction of KCBP with tubulin subunits a nd this modulation is due to the calmodulin-binding domain in the KCBP . Calcium-dependent calmodulin modulation of KCBP interaction with tub ulin suggests regulation of KCBP function by calcium, the first such r egulation of a kinesin heavy chain among all the known kinesin-like pr oteins.