Prion protein NMR structures of chickens, turtles, and frogs

Abstract

The NMR structures of the recombinant prion proteins from chicken (Gallus gallus; chPrP), the red-eared slider turtle (Trachemys scripta; tPrP), and the African clawed frog (Xenopus laevis; xlPrP) are presented. The amino acid sequences of these prion proteins show Ϸ30% identity with mammalian prion proteins. All three species form the same molecular architecture as mammalian PrP C , with a long, flexibly disordered tail attached to the N-terminal end of a globular domain. The globular domain in chPrP and tPrP contains three ␣-helices, one short 310-helix, and a short antiparallel ␤-sheet. In xlPrP, the globular domain includes three ␣-helices and a somewhat longer ␤-sheet than in the other species. The spatial arrangement of these regular secondary structures coincides closely with that of the globular domain in mammalian prion proteins. Based on the low sequence identity to mammalian PrPs, comparison of chPrP, tPrP, and xlPrP with mammalian PrP C structures is used to identify a set of essential amino acid positions for the preservation of the same PrP C fold in birds, reptiles, amphibians, and mammals. There are additional conserved residues without apparent structural roles, which are of interest for the ongoing search for physiological functions of PrP C in healthy organisms.nonmammalian species ͉ transmissible spongiform encephalopathy T he prion protein (PrP) has attracted a lot of interest because of its relation to transmissible spongiform encephalopathies (TSEs), which are a group of invariably fatal neurological diseases (1). Healthy organisms that do not express a prion protein, such as suitably selected transgenic laboratory animals, cannot develop a TSE (2), and the ''protein-only hypothesis'' further attributes TSE-causing infectivity to an aggregated ''scrapie form'' of PrP (PrP SC ) that has been isolated from brain tissue of diseased organisms (1). Although TSEs have only been documented for mammalian species, PrP has been identified in a wider range of higher organisms, which on an evolutionary scale extends at least down to amphibians (3-9). In apparent contrast to the high sequence conservation among mammalian PrPs, no physiological function has been reliably attributed to the ''cellular form'' of PrP (PrP C ) found in healthy organisms.In view of its critical role in TSEs, the prion protein has also attracted considerable interest by structural biologists. So far, atomic resolution structure determination was focused on recombinant mammalian prion proteins (10-18), which have recently been shown to represent the protein architecture of PrP C (19). As a group, the mammalian PrPs have Ϸ90% sequence identity (4). Here, we present the NMR structures of recombinant PrP from chicken, turtle, and frog (chPrP, tPrP, and xlPrP, respectively), each of which has Ϸ30% sequence identity with mammalian PrP. We then exploit this low homology in searches, based on comparison of the three-dimensional structures, for conserved amino acids with apparent roles in maintaining a common PrP C -fold, and for nonst...

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Dynamics of a truncated prion protein, PrP(113–231), from 15N NMR relaxation: Order parameters calculated and slow conformational fluctuations localized to a distinct region

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