Scheme of the regulatory sequence in the cytosolic C-terminal coiled-coil (CC)-domain in human occludin depicting the casein kinase 2 (CK2) phosphorylation (~P) sites. The CC-domain is illustrated by the shaded area calculated from the molecular surface of the crystal structure . The N-terminal part, not resolved by crystallography, is displayed as chain of amino acid circles. Interestingly, various posttranslational modifications (arrowheads) are described in close proximity to the CC-domain within the sequence 398–409 [15, 19] including the phosphorylation sites of CK2 (bold arrows), PKCs, Y398 as a c-src phophorylation site and C409 involve in disulfide bond formation. We hence call this segment regulatory pre-sequence of the CC-domain (orange). The link between pre-sequence and the actual CC-helix is thought to function as spacer (yellow). The alignment exhibits that both sequences are highly conserved. The human sequence 407–522 is resistant to proteolytic cleavage . Thus, regulatory pre-sequence, spacer and CC-helix can be considered as functional element.