Imits of the b-strands, the domain-swap stagger of the b-strands, the twist of the b-strands with respect to the fibril axis, and the organization of the foundational cross-bsheet into higher-order structure [10?2,14]. Hydrogen exchange (HX) Title Loaded From File Protection provides information on the location and stability of protein Title Loaded From File secondary structure. When a protein is dissolved in deuterium oxide (D2O), amide protons exchange with deuterons at rates determined by intrinsic factors such as pH, temperature, and the protein sequence [15]. HX can be slowed markedly when amide protons are involved in hydrogen-bonded structure that makes them inaccessible to solvent [16]. Consequently, HX data can identify amide protons involved in secondary structure and probe structural stability [17]. While solution nuclear magnetic resonance (NMR) studies of proteins are usually limited to proteins and complexes with molecular weights below 30?0 kDa, quenched hydrogen exchange (qHX) experiments can circumvent this size limit by transferring information on amide proton occupancy to the denatured state [18,19]. In the qHX experiment, HX is initiated by suspending amyloid fibrils in D2O. After varying periods of time, HX is quenched by flash freezing. The partially exchanged fibril samples are then lyophilized and dissolved in a strongly denaturing solvent such as 95 dimethyl sulfoxide (DMSO). The DMSO solvent serves two purposes. First, DMSO is sufficiently chaotropic to unfold most types of amyloid fibrils to monomers. Second, because DMSO is an aprotic solvent, HX from the denatured state occurs on timescales of hours compared to minutesHydrogen Exchange in Amylin Fibrilsor seconds in H2O, allowing the detection of amide protons trapped in the fibril. The qHX technique was first described for model amyloid fibrils formed by the Escherichia coli protein CspA. Since the method was first published [18] it has been used to study a number of amyloid fibrils relevant to human disease [9,20?6]. These include b-microglobulin [21], Ab [22,24], a-synuclein [25], prion protein [20], cystatin [23] and apolipoprotein [26]. Here, qHX is used to investigate amyloid fibrils formed by amylin. The pattern of amide proton protection in amylin fibrils is consistent with the location of the two b-strands in structural models from ssNMR [10], except the protection data suggests the strands are slightly longer, with strand b2 extending further into the `amyloidogenic segment’ consisting of residues S20 through S29 [27,28]. Protection is less consistent with an alternative model derived from EPR data [11]. Strand b1 shows less extensive protection than b2, an observation that appears to be related to the supramolecular packing of b-sheets, with strand b2 15900046 buried in the center of the protofilament structure and b1 exposed on the surface. Molecular dynamics (MD) simulations based on the ssNMR model of amylin fibrils, are used to test the hypothesis that increased motional flexibility accounts for the decreased amide proton protection observed for strand b1.observed when the lyophilized supernatant or the lyophilized fibrils were resuspended in H2O. This indicated that negligible amounts of monomeric amylin remained in the supernatant, and that species with molecular weights detectable by NMR did not dissociate from the fibrils during lyophilization. (3) In marked contrast, NMR signals were detected when the experiment was repeated, and the lyophilized pellet was taken up in 95 DMSO/ 5 DCA rather.Imits of the b-strands, the domain-swap stagger of the b-strands, the twist of the b-strands with respect to the fibril axis, and the organization of the foundational cross-bsheet into higher-order structure [10?2,14]. Hydrogen exchange (HX) protection provides information on the location and stability of protein secondary structure. When a protein is dissolved in deuterium oxide (D2O), amide protons exchange with deuterons at rates determined by intrinsic factors such as pH, temperature, and the protein sequence [15]. HX can be slowed markedly when amide protons are involved in hydrogen-bonded structure that makes them inaccessible to solvent [16]. Consequently, HX data can identify amide protons involved in secondary structure and probe structural stability [17]. While solution nuclear magnetic resonance (NMR) studies of proteins are usually limited to proteins and complexes with molecular weights below 30?0 kDa, quenched hydrogen exchange (qHX) experiments can circumvent this size limit by transferring information on amide proton occupancy to the denatured state [18,19]. In the qHX experiment, HX is initiated by suspending amyloid fibrils in D2O. After varying periods of time, HX is quenched by flash freezing. The partially exchanged fibril samples are then lyophilized and dissolved in a strongly denaturing solvent such as 95 dimethyl sulfoxide (DMSO). The DMSO solvent serves two purposes. First, DMSO is sufficiently chaotropic to unfold most types of amyloid fibrils to monomers. Second, because DMSO is an aprotic solvent, HX from the denatured state occurs on timescales of hours compared to minutesHydrogen Exchange in Amylin Fibrilsor seconds in H2O, allowing the detection of amide protons trapped in the fibril. The qHX technique was first described for model amyloid fibrils formed by the Escherichia coli protein CspA. Since the method was first published [18] it has been used to study a number of amyloid fibrils relevant to human disease [9,20?6]. These include b-microglobulin [21], Ab [22,24], a-synuclein [25], prion protein [20], cystatin [23] and apolipoprotein [26]. Here, qHX is used to investigate amyloid fibrils formed by amylin. The pattern of amide proton protection in amylin fibrils is consistent with the location of the two b-strands in structural models from ssNMR [10], except the protection data suggests the strands are slightly longer, with strand b2 extending further into the `amyloidogenic segment’ consisting of residues S20 through S29 [27,28]. Protection is less consistent with an alternative model derived from EPR data [11]. Strand b1 shows less extensive protection than b2, an observation that appears to be related to the supramolecular packing of b-sheets, with strand b2 15900046 buried in the center of the protofilament structure and b1 exposed on the surface. Molecular dynamics (MD) simulations based on the ssNMR model of amylin fibrils, are used to test the hypothesis that increased motional flexibility accounts for the decreased amide proton protection observed for strand b1.observed when the lyophilized supernatant or the lyophilized fibrils were resuspended in H2O. This indicated that negligible amounts of monomeric amylin remained in the supernatant, and that species with molecular weights detectable by NMR did not dissociate from the fibrils during lyophilization. (3) In marked contrast, NMR signals were detected when the experiment was repeated, and the lyophilized pellet was taken up in 95 DMSO/ 5 DCA rather.
