Lysine Oxidation by LOXL2 in Single Strands Versus Triple Helices: Implications for Collagen-Related Diseases

Collagen cross-linking is essential for the structural integrity of the extracellular matrix. In several pathological conditions, the triple-helical core of collagen is disrupted, and proline-rich single strands occur. Lysyl oxidases (LOXs), enzymes that initiate cross-linking by catalyzing the oxidative deamination of lysine to allysine residues, are upregulated in disease. Surprisingly little is known about the selectivity of LOXs. LOX-initiated cross-linking is believed to occur exclusively in the unstructured terminal domains of collagen, the telopeptides. But is this really the case? Herein, we show, with a combination of tailored chemical probes, enzymatic assays, CD and NMR spectroscopic analyses, that LOXL2 oxidizes Lys in proline-rich single strands but not in triple helices. A comparison of Lys-containing collagen model peptides (CMPs) with Lys-containing telopeptides revealed comparable or higher oxidation rates in proline-rich segments. The data suggest that LOXL2-initiated cross-linking occurs in pathologically disrupted triple-helical domains, offering insights into aberrant extracellular matrix stiffening.