For amylin pathology [5?]. Even if fibrils are not the main culprits, their properties are important to understand since they could serve as a reservoir from which toxic oligomers dissociate [9]. The structure of amylin fibrils has been characterized by solidstate nuclear magnetic resonance (ssNMR) [10], electron paramagnetic resonance (EPR) [11], two-dimensional infrared spectroscopy (2DIR) [12] and cryo-electron microscopy (cryo-EM) [10,11,13]. The consensus from these studies is that the amylin monomers adopt a hairpin structure composed of two HIF-2��-IN-1 site b-strands in the fibrils. Each of the b-strands forms 22948146 an intermolecular CP21 web parallel b-sheet pairing with the equivalent 12926553 b-strand from an adjacent amylin monomer. Two stacks of b-hairpins related by C2symmetry run in opposite directions along the length of the fibril and pack against each other to form the protofilament building block of the fibrils [10]. As with other amyloid fibrils, more subtle aspects of the structure are less clear and show 
larger differencesbetween models obtained by different techniques. These include the precise sequence limits 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,.For amylin pathology [5?]. Even if fibrils are not the main culprits, their properties are important to understand since they could serve as a reservoir from which toxic oligomers dissociate [9]. The structure of amylin fibrils has been characterized by solidstate nuclear magnetic resonance (ssNMR) [10], electron paramagnetic resonance (EPR) [11], two-dimensional infrared spectroscopy (2DIR) [12] and cryo-electron microscopy (cryo-EM) [10,11,13]. The consensus from these studies is that the amylin monomers adopt a hairpin structure composed of two b-strands in the fibrils. Each of the b-strands forms 22948146 an intermolecular parallel b-sheet pairing with the equivalent 12926553 b-strand from an adjacent amylin monomer. Two stacks of b-hairpins related by C2symmetry run in opposite directions along the length of the fibril and pack against each other to form the protofilament building block of the fibrils [10]. As with other amyloid fibrils, more subtle aspects of the structure are less clear and show larger differencesbetween models obtained by different techniques. These include the precise sequence limits 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,.