Effects of heme-PrP complex on cell-free conversion and peroxidase-linked immunodetection of prions in blood-based assays

•Direct interaction between heme and PrP leads to enhanced peroxidase activity.•Catalytic potential of heme-PrP complex can interfere with peroxidase-based immunodetection of PrPSc.•Heme protects PrPC from abnormal structural changes.•Heme can inhibit cell-free seeded conversion of PrPC into PrPSc.

Prion protein (PrP) binding to natural and synthetic porphyrins has been previously demonstrated but the effects of endogenous heme interactions with PrP remain uncertain. This study investigated implications of this interaction in blood-based peroxidase-linked prion immunodetection and seeded conversion of cellular prion (PrPC) into disease associated form (PrPSc). Heme binding to recombinant PrPC enhanced intrinsic peroxidase activity (POD) by 2.5-fold and POD inherent to denatured blood accounted for over 84% of luminol-based substrate oxidation in a prion immunodetection assay. An immuno-capture assay showed that 75-98% of blood POD was attributable to binding of PrPC with endogenous heme. Additionally, 10 μM heme inhibited (P < 0.05) the seeded conversion of PrPC to PrPSc through the protein misfolding cycling amplification assay. We conclude that the observed effects can interfere with cell-free conversion and peroxidase-linked immunodetection of prions in blood-based assays. These results indicate that heme-PrP interactions could modulate intrinsic POD and protect PrPC from conversion into PrPSc.