Evolutionary Origins of C-Terminal (GPP)n 3-Hydroxyproline Formation in Vertebrate Tendon Collagen

David M. Hudson,David R. Eyre,Rachel Werther,Jiann-Jiu Wu,MaryAnn Weis,Florence Ruggiero

doi:10.1371/journal.pone.0093467

David M. Hudson, David R. Eyre + Show 4 more

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https://doi.org/10.1371/journal.pone.0093467

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Journal: PloS one	Publication Date: Apr 2, 2014
Citations: 20	License type: CC BY 4.0

Affiliation: University of Washington

Abstract

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.

Highlights

Collagens are the main structural component of animal tissues and represent about a third of all proteins in the human body
Sequence alignments from the Ensembl database reveal that the (GPP)n motif is highly conserved in fibrillar collagens (Figure 1)
According to the Ensembl database, the earliest recognized Aclade fibrillar collagen is in the pre-vertebrate chordate, Ciona intestinalis (Figure 1)

Summary

Introduction

Collagens are the main structural component of animal tissues and represent about a third of all proteins in the human body. Type I collagen molecules consist of three polypeptide a-chains, approximately 1000 residues in length, each with repeating GlyXaa-Yaa primary amino acid sequences folded into the defining triple helical conformation of collagen [2]. Type I collagen is a heterotrimer of two a1 and one a2 chains. Type I collagen gene products exhibit clear tissue-specific properties despite having an identical primary sequence in all tissues. Posttranslational and processing variations in collagen chain biosynthesis are a significant source of these structural and functional differences. Cross-linking chemistry and posttranslational variations are distinct between type I collagens from skin, tendon and bone [5,6]. Collagen glycosylation and cross-linking properties can vary within the same tissue during growth and development [7,8]

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