Identification of a Proprotein Convertase Cleavage Site Within Peroxidasin and Its Regulation of Enzymatic Function

Extracellular matrix is the foundation upon which all tissues are built. The basement membrane of cells in one form of extracellular matrix that’s comprised of mainly type IV collagen. Peroxidasin (Pxdn), a matrix-bound protein, is the enzyme responsible for the catalysis of the sulfilimine bond that structurally reinforces the collagen IV network within the extracellular matrix of tissues. Loss of Pxdn in mice leads to basement membrane mechanical instability. The diminished collagen IV sulfilimine cross-links lead to reduced renal tubular basement membrane stiffness. Although catalytic function of Pxdn is known, the regulation of its targeting to the matrix and function within this structural component remains unclear. In this work we show through C-terminal sequencing, inhibitory studies, and mutational analysis that Pxdn is proteolytically processed by a proprotein convertase at the c-terminal end of the protein immediately following the amino acid Arg1336. The lack of this proteolytic processing both reduces Pxdn’s enzymatic activity and its ability to deposit into the extracellular matrix. These findings suggest that Pxdn requires activation by a proprotein convertase for complete enzymatic function within the extracellular matrix. The lack of proteolytic processing of Pxdn leads to the loss of sulfilimine crosslinks which are critical for basement membrane and tissue integrity