The NMR structures of the recombinant human prion protein, hPrP(23-230), and two C-terminal fragments, hPrP(90 -230) and hPrP(121-230), include a globular domain extending from residues 125-228, for which a detailed structure was obtained, and an N-terminal flexibly disordered ''tail.'' The globular domain contains three ␣-helices comprising the residues 144 -154, 173-194, and 200 -228 and a short anti-parallel ␤-sheet comprising the residues 128 -131 and 161-164. Within the globular domain, three polypeptide segments show increased structural disorder: i.e., a loop of residues 167-171, the residues 187-194 at the end of helix 2, and the residues 219 -228 in the C-terminal part of helix 3. The local conformational state of the polypeptide segments 187-193 in helix 2 and 219 -226 in helix 3 is measurably influenced by the length of the N-terminal tail, with the helical states being most highly populated in hPrP(23-230). When compared with the previously reported structures of the murine and Syrian hamster prion proteins, the length of helix 3 coincides more closely with that in the Syrian hamster protein whereas the disordered loop 167-171 is shared with murine PrP. These species variations of local structure are in a surface area of the cellular form of PrP that has previously been implicated in intermolecular interactions related both to the species barrier for infectious transmission of prion disease and to immune reactions. P rion proteins (PrP) are associated with transmissible spongiform encephalopathies (TSE), which are invariably fatal diseases characterized by loss of motor control, dementia, and paralysis wasting (1, 2). Human TSEs include Creutzfeldt-Jakob disease, fatal familial insomnia, the Gerstmann-Sträussler-Scheinker syndrome, and kuru, and there is bovine spongiform encephalopathy in cattle and scrapie in sheep. The ''proteinonly'' hypothesis (3, 4) proposes that TSEs are caused by the conversion of a ubiquitous ''cellular form'' of PrP (PrP C ) into an aggregated ''scrapie form'' (PrP Sc ). According to this model, the prion protein (PrP) would at the same time be target and infectious agent in TSEs, which could explain that this class of diseases can be traced to infectious, inherited, and spontaneous origins (2, 5). PrP Sc is characterized by a high ␤-sheet content, insolubility in detergents, and resistance to proteolysis in its aggregated form (6-8) whereas PrP C is a soluble protein with a high content of ␣-helices (8, 9) and high susceptibility to proteolytic digestion. No chemical modifications have as yet been identified by which the two PrP forms would differ (10).Considering that the protein-only hypothesis suggests a change of protein conformation as a possible cause of the onset of TSEs, the three-dimensional prion protein structures have attracted keen interest. So far, nuclear magnetic resonance (NMR) solution studies have been described for monomeric, cellular forms of PrP of the two most widely used laboratory animals in prion research, the mouse (m) and the Syrian hamster (sh)...

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Transmissible spongiform encephalopathies (TSE) or “prion diseases” have been related to the “protein‐only hypothesis”, which suggests that the “scrapie form (PrPSc)” of the prion protein (PrP) is the TSE infectious agent. The nmr structure of the ubiquitous benign cellular form of PrP (PrPC) consists of a globular domain of residues 126–231 with three α‐helices and a short β‐sheet, and a flexible extended “tail” of residues 23–125. The peptide segment of helix 1 has been implicated in various stages of hypothetical pathways to prion pathology on the basis of the protein‐only idea, including that it takes part in the conformation change that leads from PrPC to PrPSc. In this paper we describe solution nmr and circular dichroism studies of the synthetic hexadecapeptide mPrP(143–158), with the sequence H–NDWEDRYYRENMYRYP–NH2, where the bold letters represent the segment that forms helix 1 in murine PrPC. In both H2O and a 1:1 mixture of H2O and trifluoroethanol this polypeptide segment shows high helix propensity, which is a key issue in discussions on potential roles of this molecular region in conformational transitions of PrP. © 1999 John Wiley & Sons, Inc. Biopoly 51: 145–152, 1999

We describe the first direct observation of NsH‚‚‚OdC hydrogen bonding in nucleic acids via the four-bond 4h J NiNj coupling within an N1 i sH1 i ‚‚‚O6 j dC6 j -N1 j segment of a G‚G‚G‚G tetrad. The experiment, two-dimensional (2D) HN(N)-TOCSY, makes use of band-selective 15 N isotropic mixing to transfer magnetization exclusively via the 4h J NN couplings to yield correlations between N1H i (ω 2 ) and N1 j (ω 1 ) across the hydrogen-bonded segment. In a complementary experiment, 2D cross-polarization (CP)-H(N)CO-(NN)-TOCSY, employing band-selective heteronuclear 15 N-13 C cross-polarization sequences on either side of the 15 N-15 N TOCSY period, correlations are obtained between N1H i (ω 2 ) and C6 j (ω 1 ) nuclei across the hydrogen bond. The symmetric A 2 X 2 -type coupling topology of the four-spin nitrogen system in the G‚G‚G‚G tetrad permits accurate measurement of these couplings by a new procedure that fits the experimental data with known analytical isotropic mixing transfer functions. The techniques are demonstrated on a G‚G‚G‚G tetrad formed within a novel dimeric quadruplex fold of a uniformly 13 C/ 15 N- labeled d(G-G-G-T-T-C-A-G-G) DNA sequence. The value of the 4h J NN coupling constant for this system is estimated to be 0.136 ( 0.021 Hz.

A nuclear magnetic resonance study reveals the molecular basis of activation and regulation of the lipid kinase PIP5K by membrane lipids.

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Hydrogen-bonding interactions are fundamentally important in the stabilization of biomolecular secondary structure elements and in defining the globular folds of polypeptide and RNA chains. In particular, they very often play a key role in enzymatic and ribozyme activities and are a fundamental element in biomolecular recognition events. 1 The recent direct detection of scalar couplings between hydrogen donor and acceptor moiety spins in both nucleic acids 2-6 and proteins 7-10 by NMR, has opened a new approach for monitoring intramolecular hydrogen bonds and provided invaluable parameters for the characterization of structure and dynamics of biological macromolecules in solution by NMR. Of significant interest is the possibility of detecting intermolecular hydrogen bonds at macromolecular interfaces such as in proteinprotein and protein-nucleic acid complexes. In this contribution, we report the direct NMR observation of intermolecular hydrogen bonds between the guanidinium groups of arginines in the 16mer arginine-rich HTLV-1 Rex peptide (Figure S1a, Supporting Information) and the major groove edges of guanine bases of a 33-mer RNA aptamer (Figure S1b), whose solution structure was solved recently by NMR in our laboratory. 12 This NOE-based solution structure established that the side-chain guanidinium groups of all the six arginine residues are involved in either electrostatic or hydrogen bonding interactions with the RNA target. The guanidinium groups of arginines R6, R9, and R10, are within 4 Å from one or more backbone phosphates on the RNA aptamer. The guanidinium groups of R5, R7, and R13 form