Insights on the Evolution of Prolyl 3-Hydroxylation Sites from Comparative Analysis of Chicken and Xenopus Fibrillar Collagens

David M Hudson,David R Eyre,Maryann Weis,Bostjan Kobe

doi:10.1371/journal.pone.0019336

Abstract

Recessive mutations that prevent 3-hydroxyproline formation in type I collagen have been shown to cause forms of osteogenesis imperfecta. In mammals, all A-clade collagen chains with a GPP sequence at the A1 site (P986), except α1(III), have 3Hyp at residue P986. Available avian, amphibian and reptilian type III collagen sequences from the genomic database (Ensembl) all differ in sequence motif from mammals at the A1 site. This suggests a potential evolutionary distinction in prolyl 3-hydroxylation between mammals and earlier vertebrates. Using peptide mass spectrometry, we confirmed that this 3Hyp site is fully occupied in α1(III) from an amphibian, Xenopus laevis, as it is in chicken. A thorough characterization of all predicted 3Hyp sites in collagen types I, II, III and V from chicken and xenopus revealed further differences in the pattern of occupancy of the A3 site (P707). In mammals only α2(I) and α2(V) chains had any 3Hyp at the A3 site, whereas in chicken all α-chains except α1(III) had A3 at least partially 3-hydroxylated. The A3 site was also partially 3-hydroxylated in xenopus α1(I). Minor differences in covalent cross-linking between chicken, xenopus and mammal type I and III collagens were also found as a potential index of evolving functional differences. The function of 3Hyp is still unknown but observed differences in site occupancy during vertebrate evolution are likely to give important clues.

Highlights

Fibrillar collagens are found throughout all metazoan phyla
Collagens undergo many post-translational modifications, such as the conversion of approximately 50% of all prolyl residues to (4R, 2S-L-hydroxyproline; 4Hyp), which make up approximately a quarter of the amino acid content of most fibrillar a-chains [1]
The A3 site is partially 3hydroxylated in xenopus a1(I) and all chicken A-clade a-chains except a1(III)

Summary

Introduction

Fibrillar collagens are found throughout all metazoan phyla. Collagen is the most abundant animal protein, with 28 or more different collagen types produced by over 40 genes in vertebrates [1,2]. Collagens undergo many post-translational modifications, such as the conversion of approximately 50% of all prolyl residues to (4R, 2S-L-hydroxyproline; 4Hyp), which make up approximately a quarter of the amino acid content of most fibrillar a-chains [1]. 25% or more of lysine residues are hydroxylated to 5-hydroxylysine, some of which are glycosylated. It is well established that these post-translational modifications enhance collagen structural stability [3,4]. The function of the much less frequent 3-hydroxylation of proline in the collagen a1(I) chain to form 3-hydroxyproline (3S, 2S-Lhydroxyproline; 3Hyp) is unclear [5]

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Conclusion