Decoding the comprehensive substrate-specificity and evidence of altered site-specific collagen prolyl-3-hydroxylation, lysyl-hydroxylation, and lysyl O-glycosylation in P4ha1 and P4ha2 deleted mutant mice

Collagens, the most abundant proteins in mammals, play pivotal roles in the maintenance of tissue structure, functions, cell-to-cell communication, cellular migration, behavior, and growth. Collagens are highly complex in structure due to the dynamic post-translational modifications (PTMs) such as hydroxylations (on prolines and lysine residues) and O-glycosylation (on hydroxylysines) enzymatically catalyzed during biosynthesis. The most prevalent modification in fibrillar collagens is prolyl 4-hydroxylation catalyzed by collagen prolyl 4-hydroxylases (C-P4hs). Prolyl 4-hydroxylation on collagens plays a critical role in collagen biosynthesis, thermostability, and cell-collagen interactions. However, the site-specificity of prolyl 4-hydroxylase 1 (P4ha1) and P4ha2 is not comprehensively studied yet. Further, the effect of P4ha1 and P4ha2 on the plethora of other site-specific collagen PTMs is not known to date. In-depth mass-spectrometry data (PXD008802) analysis of mice skin collagen I extracted from wild-type and different deletion mutants of C-P4hs revealed that partial or full deletion of prolyl 4-hydroxylases (P4ha1 and P4ha2) significantly decreases collagen deposition in ECM hinting towards perturbed biosynthesis. A total of 421 site-specific PTMs on fibrillar collagen chains (Col1a1, Col1a2, and Col3a1) were identified. Further, novel 23 P4ha1 specific, 8 P4ha2 specific, and 18 C-P4hs promiscuous sites on fibrillar collagen chains were identified. Partial deletion of P4ha1 and full deletion of P4ha2 also resulted in altered levels of the site-specific prolyl-3-hydroxylation occupancy in collagen I. Surprisingly, an increased level of site-specific lysyl hydroxylation (Col1a1-K731, Col1a2-K183,315) was documented upon partial deletion of P4ha1 and full deletion of P4ha2. Our findings showcased that the activity of prolyl 4-hydroxylases is not limited to 4-hydroxylation of specific proline sites, but simultaneously can perturb the entire biosynthetic network by modulating prolyl 3-hydroxylation and lysyl hydroxylation occupancy levels in the fibrillar collagen chains in a site-specific manner.