Evolutionary origins of C-terminal (GPP)n 3-hydroxyproline formation in vertebrate tendon collagen.
Approximately half the proline residues in fibrillar collagen are hydroxylated. The predominant form is 4-hydroxyproline, which helps fold and stabilize the triple helix. A minor form, 3-hydroxyproline, still has no clear function. Using peptide mass spectrometry, we recently revealed several previously unknown molecular sites of 3-hydroxyproline in fibrillar collagen chains. In fibril-forming A-clade collagen chains, four new partially occupied 3-hydroxyproline sites were found (A2, A3, A4 and (GPP)n) in addition to the fully occupied A1 site at Pro986. The C-terminal (GPP)n motif has five consecutive GPP triplets in α1(I), four in α2(I) and three in α1(II), all subject to 3-hydroxylation. The evolutionary origins of this substrate sequence were investigated by surveying the pattern of its 3-hydroxyproline occupancy from early chordates through amphibians, birds and mammals. Different tissue sources of type I collagen (tendon, bone and skin) and type II collagen (cartilage and notochord) were examined by mass spectrometry. The (GPP)n domain was found to be a major substrate for 3-hydroxylation only in vertebrate fibrillar collagens. In higher vertebrates (mouse, bovine and human), up to five 3-hydroxyproline residues per (GPP)n motif were found in α1(I) and four in α2(I), with an average of two residues per chain. In vertebrate type I collagen the modification exhibited clear tissue specificity, with 3-hydroxyproline prominent only in tendon. The occupancy also showed developmental changes in Achilles tendon, with increasing 3-hydroxyproline levels with age. The biological significance is unclear but the level of 3-hydroxylation at the (GPP)n site appears to have increased as tendons evolved and shows both tendon type and developmental variations within a species.
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
David M
DM
Hudson
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
Rachel
R
Werther
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
MaryAnn
M
Weis
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
Jiann-Jiu
JJ
Wu
Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, United States of America.
David R
DR
Eyre
D000595:Amino Acid Sequence; D000818:Animals; D001842:Bone and Bones / Q000378:metabolism; D002417:Cattle; D002645:Chickens / Q000378:metabolism; D024042:Collagen Type I / Q000378:metabolism*; D024043:Collagen Type II / Q000378:metabolism*; D019143:Evolution, Molecular; D024022:Fibrillar Collagens / Q000378:metabolism; D006801:Humans; D006900:Hydroxylation / Q000502:physiology; D006909:Hydroxyproline / Q000378:metabolism*; D007798:Lampreys / Q000378:metabolism; D017434:Protein Structure, Tertiary; D013710:Tendons / Q000378:metabolism*; D014714:Vertebrates / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism
D024042:Collagen Type I; D024043:Collagen Type II; D024022:Fibrillar Collagens; C026215:3-hydroxyproline; D006909:Hydroxyproline