Interaction of calmodulin with the cytoplasmic domain of platelet glycoprotein VI

The platelet collagen receptor, glycoprotein VI (GPVI) and GPIb-IX-V which binds von Willebrand factor, initiate platelet aggregation at low or high shear stress, respectively. We recently reported that positively charged, membrane-proximal sequences within cytoplasmic domains of GPIbbeta and GPV of GPIb-IX-V bind calmodulin. We now show that GPV also binds calmodulin as follows-(1) calmodulin coimmunoprecipitated with GPVI from resting platelet lysates using an anti-GPVI IgG, but partially dissociated in platelets activated by collagen or collagen-related peptide; (2) calmodulin coprecipitated from platelet lysates with maltose-binding protein (MBP)-GPVI cytoplasmic domain fusion protein, but not MBIP alone; (3) GPVI-related synthetic peptide based on the membrane-proximal sequence, His269-Pro287, induced a shift in calmodulin migration on nondenaturing gels, an assay that identifies calmodulin-binding peptides. His269-Pro287 is analogous to the calmodulin-binding sequence in GPIbbeta. The novel interaction of GPVI and calmodulin may regulate aspects of GPVI function. (C) 2002 by The American Society of Hematology.