Multidomain human peroxidasin 1 is a highly glycosylated and stable homotrimeric high-spin ferric peroxidase

Human peroxidasin 1 (hsPxd01) is a multidomain heme peroxidase that uses bromide as a cofactor for the formation of sulfilimine crosslinks. The latter confer critical structural reinforcement to collagen IV scaffolds. Here hsPxd01 and various truncated variants lacking non-enzymatic domains were recombinantly expressed in HEK cell lines. The N-glycosylation site occupancy and disulfide pattern, the oligomeric structure and unfolding pathway are reported. The homotrimeric ironprotein contains a covalently-bound ferric high-spin heme per subunit with a standard reduction potential of the Fe(III)/Fe(II) couple of -233 mV at pH 7.0. Despite sequence homology at the active site and biophysical properties similar to human peroxidases, the catalytic efficiency of bromide oxidation (kcat/KM) of full-length hsPxd01 is rather low but increased upon truncation. This is discussed with respect to its structure and proposed biosynthetic function in collagen IV crosslinking.