Structural and Mechanistic Insights into the Catalytic Versatility of Lysyl Hydroxylases in Collagen Post-Translational Modifications

Iron-dependent lysyl hydroxylases (LHs) play a pivotal role in collagen biosynthesis by catalyzing post-translational modifications (PTMs) of lysine residues. These PTMs involve site-specific hydroxylation and sequential O-glycosylation, facilitated either by LHs or by collagen galactosyltransferase (COLGALTs) enzyme complexes. Here, we present the indispensable evolutionary significance of the LH-catalyzed PTMs, i.e., collagenous lysine hydroxylation (HyK) and lysyl-O-glycosylations (G-HyK and GG-HyK) in maintaining basement membrane assembly for multi-cellular life forms. The unique structural features of LHs enable remarkable stereoselectivity and regio-specificity in these critical enzymatic reactions. However, the understanding of the active-site architectures and catalytic mechanisms governing lysyl-5-hydroxylation and O-glycosylation remains limited. In this perspective, we present a comprehensive structural analysis of the intricate amino acid networks shaping the active site and secondary structure of three isoforms of LHs (LH1, LH2, and LH3), drawing comparisons with COLGALTs (COLGALT1 and COLGALT2) to enrich structural and mechanistic understandings. Overall, the detailed domain-specific structural comparisons of LH isoforms provide a strong foundation for future mechanistic studies. These insights will aid in understanding the origins of substrate specificity, elucidating regio- and stereo-selectivity, and determining the roles of specific residues in the reactivity of LH-catalyzed post-translational modifications essential for collagen biosynthesis.