Site-specific analysis of N-glycans from different sheep prion strains

Abstract

Prion diseases are a group of neurodegenerative diseases affecting a wide range of mammalian species, including humans. During the course of the disease, the abnormally folded scrapie prion protein (PrPSc) accumulates in the central nervous system where it causes neurodegeneration. In prion disorders, the diverse spectrum of illnesses exists because of the presence of different isoforms of PrPSc where they occupy distinct conformational states called strains. Strains are biochemically distinguished by a characteristic three-band immunoblot pattern, defined by differences in the occupancy of two glycosylation sites on the prion protein (PrP). Characterization of the exact N-glycan structures attached on either PrPC or PrPSc is lacking. Here we report the characterization and comparison of N-glycans from two different sheep prion strains. PrPSc from both strains was isolated from brain tissue and enzymatically digested with trypsin. By using liquid chromatography coupled to electrospray mass spectrometry, a site-specific analysis was performed. A total of 100 structures were detected on both glycosylation sites. The N-glycan profile was shown to be similar to the one on mouse PrP, however, with additional 40 structures reported. The results presented here show no major differences in glycan composition, suggesting that glycans may not be responsible for the differences in the two analyzed prion strains.

Copper coordination modulates prion conversion and infectivity in mammalian prion proteins

“…The first two beta-sheets (beta0 and beta1) precede the first alpha-helix, then a second beta-sheet (beta2) anticipates the last two helices [ 16 ]. The latter contain a single disulphide bridge and two sites for N-glycosylation [ 17 ].…”

Prion assemblies: structural heterogeneity, mechanisms of formation, and role in species barrier

“…The stoichiometric ratio of PrP Sc glycoforms is strain-specific and faithfully maintained during prion passaging in the same host species (Collinge et al 1996 ; Somerville and Ritchie 1990 ), which means that a given strain has a specific preference for certain PrP C glycotypes. Yet, PrP Sc from different strains does not appear to differ in glycan composition (Nakic et al 2021 ), suggesting that prion SSD are not encoded in glycans. However, PrP Sc occupancy by glycans, given their extended size, variable proportion, and composition at each site (Nakic et al 2021 ; Rudd et al 2002 ), is likely to affect the stability, clearance and the dynamic of the forming assemblies by steric hindrance.…”

“…Yet, PrP Sc from different strains does not appear to differ in glycan composition (Nakic et al 2021 ), suggesting that prion SSD are not encoded in glycans. However, PrP Sc occupancy by glycans, given their extended size, variable proportion, and composition at each site (Nakic et al 2021 ; Rudd et al 2002 ), is likely to affect the stability, clearance and the dynamic of the forming assemblies by steric hindrance. Accordingly, transgenic modeling suggests that PrP C glycosylation status can influence the efficacy of intra- and inter-species transmission of prions (DeArmond et al 1997 ; Tuzi et al 2008 ; Wiseman et al 2015 ) and prion strain properties (Cancellotti et al 2013 ).…”

Redox mechanisms and their pathological role in prion diseases: The road to ruin

“…Biometals can also modulate the activity of certain enzymes involved in disease processes, ultimately slowing disease progression. In addition, an interaction between PrP C and manganese or zinc, but not copper, causes shedding of the N1 fragment of PrP C , which, in turn, impacts prion N-glycosylation and its cellular functions, distribution, cellular trafficking, aggregation, and fibril formation [ 41 , 42 ]. In the unglycosylated mutants, PrP C was localized on the cell surface and readily converted to PrP Sc , indicating that glycans are not necessary for prion infection but rather a lack of glycation favours misfolding and PrP Sc transmission [ 43 ].…”