Figure 3. Hydroxylated proline residues participate in collagen fibril formation.

They also promote interactions with cellular collagen receptors, such as integrins and DDRs, in a direct and an indirect manner. Many of the integrin and DDR recognition motifs in collagens contain 4-Hyp. Furthermore, GPO triplets may facilitate site-specific in vivo flexibility, and promote the binding of cellular receptors to motifs next to GPO-sites.