CIB1 (Calcium and Integrin Binding protein1; also calmyrin, KIP and CIBP) is a 22-23kD, Ca++ binding member of the CIB family of proteins. It is widely expressed, being found in neurons, platelets/megakaryocytes, skeletal muscle myocytes and lymphocytes. CIB1 is associated with the cytosolic side of the plasma membrane, and has multiple binding partners, including InsP3R, GPIIb aIIb, presenilin 2, and NBR1 plus FEZ. When CIB1 binds InsP3R, this ER-embedded receptor is both activated, and later desensitized to subsequent ligand binding. Relative to GPIIb, CIB1 interaction with the aIIbB 3 integrin on platelets following thrombin exposure appears to inhibit integrin activation, thus providing a tight control on subsequent platelet binding to fibrinogen. Human CIB1 is 191aa in length. It contains a utilized myristoylation site at 2aa, followed by two EF-hand domains (aa103-183). CIB1 is suggested to act as a monomer. There is at least one potential isoform variant that shows a 40aa insertion after 29aa. Full length human CIB1 (aa1-191) shares 94% aa sequence identity with mouse CIB1.