Asparagine and glutamine ladders promote cross-species prion conversion [Neurobiology]

Prion transmission between species is governed in part by primary sequence similarity between the infectious prion aggregate, PrPSc, and the cellular prion protein of the host, PrPC. A puzzling feature of prion formation is that certain PrPC sequences, such as that of bank vole, can be converted by a remarkably broad array of different mammalian prions, whereas others, such as rabbit, show robust resistance to cross-species prion conversion. To examine the structural determinants that confer susceptibility or resistance to prion conversion, we systematically tested over 40 PrPC variants of susceptible and resistant PrPC sequences in a prion conversion assay. Five key residue positions markedly impacted prion conversion, four of which were in steric zipper segments where side chains from amino acids tightly interdigitate in a dry interface. Strikingly, all 5 residue substitutions modulating prion conversion involved the gain or loss of an asparagine or glutamine residue. For 2 of 4 positions, N and Q residues were not interchangeable, revealing a strict requirement for either an N or Q residue. Bank voles have a high number of N and Q residues and a high N:Q ratio. These findings suggest that a high number of N and Q residues at specific positions may stabilize β-sheets and lower the energy barrier for crossspecies prion transmission, potentially due to hydrogen bond networks from side chain amides forming extended N/Q ladders. These data also suggest that multiple PrPC segments containing N/Q residues may act in concert along a replicative interface to promote prion conversion.

from # All Medicine by Alexandros G. Sfakianakis via Alexandros G.Sfakianakis on Inoreader http://ift.tt/2wIhzsI
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