Neuroprotective alpha-cleavage of the human prion protein significantly impacts Cu(ii) coordination at its His111 site

Abstract

The cellular prion protein (PrPC) is a copper binding protein that undergoes post-translational modifications, such as endoproteolytic alpha cleavage, which occurs in the vicinity of the His111 Cu binding site. Alpha cleavage processing of PrPC is considered to be neuroprotective since the cleavage site is located in a region that is key to the conversion of PrPC into the infectious scrapie isoform (PrPSc), yielding a membrane bound C1 fragment of PrPC that still contains His111. In this work, we use hPrP(111-115) fragment as a model peptide to evaluate the impact of alpha cleavage processing of PrPC in its ability to coordinate Cu(ii) ions at His111. By using different spectroscopic techniques such as electronic absorption, circular dichroism, nuclear magnetic resonance, and electron paramagnetic resonance, this study demonstrates that Cu(ii) binding to the cleaved His111 site is highly dependent on Cu and proton concentrations. The imidazole group of His111 and its free NH2 terminus emerge as the main anchoring sites for Cu(ii) coordination, yielding very different complexes from those characterized for the intact His111 site in the full protein. Different Cu(ii) coordination modes that could form with the alpha cleaved PrPC under physiological conditions are identified and characterized. Overall, this study contributes to understand how alpha cleavage processing of PrPC impacts its Cu(ii) binding properties at His111. While the functional implications of Cu binding to the cleaved PrPC remain to be discovered, proteolytic processing of PrPC and its Cu binding features appear to be molecular events that might be strongly linked to its cellular function.

The first report of genetic variations in the chicken prion protein gene

“…Specifically, the imidazole ring of histidine is significantly related to the interaction between PrP C and copper [28,29]. In a recent study, neuroprotective αcleavage event of PrP C significantly influences on Cu (II) coordination at its His111 site [30].…”

Structural Consequences of Copper Binding to the Prion Protein

“…By using different spectroscopic techniques, studies have also focused on the Cu(II) coordination to the C1 fragment, which includes the His111, as result of the neuroprotective alpha-cleavage [109]. By using the PrP(111–115) fragment as a model system, it was shown that the His111 and the free NH 2 group act as an anchoring site for Cu 2+ , resulting in different coordination modes, depending on proton and copper concentrations ([109] and reviewed in [110]).…”

Structural Determinants of the Prion Protein N-Terminus and Its Adducts with Copper Ions

“…The released N1 fragment may still contain the OR region and the His96 site; however, the His111 site may be significantly disturbed, as the cleavage occurs between residues that participate in Cu 2+ coordination, leaving a His111 with a free NH 2 terminal group at the membrane bound C1 fragment. A recent spectroscopic study determined the impact of α-cleavage processing on Cu 2+ binding to His111, using a model peptide for the C1 fragment [116]. Indeed, in this fragment His111 and the free NH 2 terminal group act as the main anchoring sites for Cu 2+ , resulting in coordination modes that are highly dependent on proton and copper concentrations, and are quite different from those characterized for the intact His111 site in the full protein (Figure 3).…”