Collagen and collagen-associated proteins studies on the type XV trimerization domain, prolyl 3-hydrolase and the prolyl 3-hydroxylase cartilage associated protein cyclophilin B complex

Collagen and its associated proteins are essential for proper tissue structure, and defects in either can lead to numerous diseases. While collagen triple‑helical domains are well studied, much less is known about their non‑collagenous regions. This work reports the crystal structure and biochemical properties of the non‑collagenous trimerization domain of human type XV collagen, revealing a highly stable trimer supported by hydrophobic interactions within and between monomers, capable of forming at picomolar concentrations. We also show that the endoplasmic reticulum P3H1●CRTAP●CypB complex functions as a prolyl 3‑hydroxylase, molecular chaperone, and protein disulfide isomerase, binding both unfolded and triple‑helical collagen. Despite efforts to improve yields, the complex remains unstable, limiting deeper structural characterization. These findings expand understanding of collagen assembly and the multifunctional machinery required for its biosynthesis.