A Novel Proteolytic Processing of Prolysyl Oxidase

Abstract

Lysyl oxidase (LOX) is an amine oxidase that is critical for the stability of connective tissues. The secreted proLOX is enzymatically quiescent and is activated through proteolytic cleavage between residues Gly₁₆₂ and Asp₁₆₃ (residue numbers according to the mouse LOX) by bone morphogenetic protein (BMP)-1 gene products. Here we report a novel processing of proLOX identified in vitro and in vivo. Two forms of mature LOX were identified and characterized by their immunoreactivity to specific antibodies, amine oxidase activity, and mass spectrometry. One form was identified as a well-characterized BMP-1 processed LOX protein. Another was found to be a truncated form of LOX resulting from the cleavage at the carboxy terminus of Arg₁₉₂. The truncated form of LOX still appeared to retain amine oxidase activity. The results from the proLOX gene deletion and mutation experiments indicated that the processing occurs independent of the cleavage of proLOX by BMP-1 gene products and likely requires the presence of LOX propeptide. These results indicate that proLOX could be processed by two different mechanisms producing two forms of active LOX.

• lysyl oxidase
• protein processing
• amine oxidase
• extracellular matrix

Acknowledgments

The authors thank Drs. Trackman and Palamakumbura for their valuable suggestions for LOX purification and activity assay and Drs. Csiszar and Fong for providing the αLOXh antibody. This work was supported by NIH-NIDCR R21 DE019569.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.