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hEGF, or human growth factor-like EGF, domains have sixconserved residues disulfide-bonded into the characteristic 'ababcc' pattern. They are involved in growth and proliferation of cells, in proteins of the Notch/Delta pathway, neurogulin and selectins. hEGFs are also found in mosaic proteins with four-disulfide laminin EGFs such as aggrecan and perlecan. The core fold of the EGF domain consists of two small beta-hairpins packed against each other. Two major structural variants have been identified based on the structural context of the C-terminal Cys residue of disulfide 'c' in the C-terminal hairpin: hEGFs and cEGFs. In hEGFs the C-terminal thiol resides in the beta-turn, resulting in shorter loop-lengths between the Cys residues of disulfide 'c', typically C[8-9]XC. These shorter loop-lengths are also typical of the four-disulfide EGF domains, laminin ad integrin. Tandem hEGF domains have six linking residues between terminal cysteines of adjacent domains. hEGF domains may or may not bind calcium in the linker region. hEGF domains with the consensus motif CXD4X[F,Y]XCXC are hydroxylated exclusively in the Asp residue.
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