Binds both calcium and zinc. May be involved in calcium-dependent cuticle cell differentiation, hair shaft and hair cuticular barrier formation. Homodimer and homotetramer for the citrullinated form. Skin specific, specifically expressed at the inner endocuticle of hair fibers. More than half of the arginine residues undergo citrullination by PAD1 and PAD2. Arg-51 is specifically citrullinated by PAD3 and promotes tetramerization. Belongs to the S-100 family.