Prion protein—Semisynthetic prion protein (PrP) variants with posttranslational modifications

Abstract

Deciphering the pathophysiologic events in prion diseases is challenging, and the role of posttranslational modifications (PTMs) such as glypidation and glycosylation remains elusive due to the lack of homogeneous protein preparations. So far, experimental studies have been limited in directly analyzing the earliest events of the conformational change of cellular prion protein (PrPC) into scrapie prion protein (PrPSc) that further propagates PrPC misfolding and aggregation at the cellular membrane, the initial site of prion infection, and PrP misfolding, by a lack of suitably modified PrP variants. PTMs of PrP, especially attachment of the glycosylphosphatidylinositol (GPI) anchor, have been shown to be crucially involved in the PrPSc formation. To this end, semisynthesis offers a unique possibility to understand PrP behavior in vitro and in vivo as it provides access to defined site‐selectively modified PrP variants. This approach relies on the production and chemoselective linkage of peptide segments, amenable to chemical modifications, with recombinantly produced protein segments. In this article, advances in understanding PrP conversion using semisynthesis as a tool to obtain homogeneous posttranslationally modified PrP will be discussed.

Virus Infection, Genetic Mutations, and Prion Infection in Prion Protein Conversion

“…PrP C is a host-encoded glycoprotein tethered to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor moiety and expressed most abundantly in the brain, particularly by neurons, and to lesser extents in other non-neuronal tissues, including heart, lung, pancreas, liver, spleen, testis, and kidney [25][26][27]. Many physiological functions have been suggested for PrP C , including oxidative stress mitigation, neuroprotection, and those associated with cell trafficking, cell adhesion, cell differentiation, cell signaling, and cell survival [28].…”

“…PrP C structurally consists of two domains; the flexible non-structural N-terminal domain including the so-called octapeptide repeat (OR) region in the middle, and the globular C-terminal domain with 2 short β-sheets and 3 α-helices [26,27]. Mouse PrP C is translated as a precursor protein comprised of 254 amino acids, with the 22 amino acids of an endoplasmic reticulum (ER) migration signal sequence at the N-terminus and the 23 amino acids of a GPI anchor addition signal sequence at the C-terminus [26,27]. Both signal sequences are removed in the ER as the nascently translated PrP enters the ER [26,27].…”

“…Mouse PrP C is translated as a precursor protein comprised of 254 amino acids, with the 22 amino acids of an endoplasmic reticulum (ER) migration signal sequence at the N-terminus and the 23 amino acids of a GPI anchor addition signal sequence at the C-terminus [26,27]. Both signal sequences are removed in the ER as the nascently translated PrP enters the ER [26,27]. The C-terminal domain further undergoes posttranslational modifications, such as disulfide bond formation between cysteine residues at positions 178 and 213 and N-type sugar chain addition at asparagine residues of positions 180 and 196 [26,27].…”

N-Terminal Regions of Prion Protein: Functions and Roles in Prion Diseases

“…The gene for PrP C , termed Prnp , in human and mouse consists of 2 and 3 exons and resides on chromosome 20 and 2, respectively. The protein coding sequence lies within the last single exon [ 17 , 18 ]. PrP C is synthesized as a precursor protein in the endoplasmic reticulum (ER).…”

“…PrP C is synthesized as a precursor protein in the endoplasmic reticulum (ER). The N-terminal and C-terminal sequences, which are rich in hydrophobic residues, are removed as a signal peptide sequence and a GPI-anchor signal sequence, respectively, in the ER ( Figure 1 A) [ 17 , 18 ]. PrP C also undergoes several post-translational modifications en route to the cell surface, including a GPI anchor attachment at the C-terminus, N -glycosylation at two sites, and formation of a disulfide bond in the C-terminal domain ( Figure 1 A) [ 19 , 20 , 21 , 22 , 23 , 24 ].…”