Pcdp1 is the mammalian orthologue of FAP221. (A) Diagram comparing the FAP221 and Pcdp1 protein coding sequences that share two major regions of identity. In the second region (shown in blue), both proteins have a predicted CaM-binding site (hatch marked region labeled “CaM”). Pcdp1 also has a predicted IQ motif at its C terminus (IQ). Regions that were expressed and used in the CaM gel overlay assay are marked with a black line; A and B for FAP221 and 1 and 2 for Pcdp1. (B) CaM gel overlay assay of FAP221 and Pcdp1 predicted CaM-binding regions. Overlays were performed with CaM from mouse (mCaM). The predicted CaM-binding regions shown in hatch marks only bind to CaM in the presence of high calcium. The predicted IQ motif at the C terminus of Pcdp1 does not bind to CaM under high or low calcium conditions. (C) Site-directed mutagenesis was used to alter three amino acids in the FAP221 CaM-binding site. Gel overlay analysis demonstrates the altered CaM-binding site no longer binds to C. reinhardtii CaM (CrCaM) in the presence of calcium.