Abstract
Drosophila calcium/calmodulin-dependent protein kinase II is alternatively spliced to generate multiple isoforms that vary only in a region between the calmodulin-binding domain and the association domain. This variation has been shown to modulate activation of the enzyme by calmodulin. In this study we examine the ability of seven of the
Drosophila isoforms to phosphorylate purified protein substrates and to be inhibited by a substrate analog, and the response of six of the isoforms to a mutant form of calmodulin (V91G) that was isolated in a genetic screen. Significant variation in
K
m
s for Eag, a potassium channel, and Adf-1, a transcription factor, were found. In the case of the a peptide inhibitor, AC3I, there were significant variations in
K
i between isoforms.
K
act for V91G calmodulin was increased for all of the isoforms. In addition, one isoform, R1, exhibited a lower
V
max when assayed with this mutant CaM. These results indicate that the variable domain of calcium/calmodulin-dependent protein kinase II is capable of altering the substrate specificity of the catalytic domain and the activation response to calmodulin.