Nditions for the qHX experiments. (1) To start, 0.1 mg lyophilized, un-fibrillized 15 N amylin was dissolved in 220 ml 95 DMSO/5 DCA at an apparent pH measured in DMSO (pH*) of 3.5, to give an amylin concentration of 0.12 mM. The heteronuclear single-quantum correlation (1H-15N HSQC) spectrum obtained at 25uC showed that amylin is soluble, monomeric, unfolded, and thus amenable to NMR spectroscopy. The spectrum showed no changes after 1 month at room temperature, demonstrating amylin is stable in 95 DMSO. 25033180 Additional pulse-field gradient translational diffusion NMR experiments [29] showed that amylin in DMSO has an ?apparent hydrodynamic radius of 1561 A, close to the expected ?value of 17 A for an unfolded monomer (Figure S1). (2) Next, it was determined that negligible amounts of 15N-amylin monomers remain in solution when amylin undergoes fibrillization, and that lyophillization does not disrupt the fibrils. A 0.12 mM 15N-amylin sample in H2O buffer containing 10 mM sodium phosphate pH 7.4 with 10 (v/v) acetonitrile was fibrillized without agitation for 4 days at 37uC. Electron microscopy (EM) images of fibrils grown under these conditions are shown in Figure S2. Amylin fibrils were sedimented at 15,000 g for 30 min. The supernatant, and pellet resuspended in H2O, were flash-frozen in a dry ice/ ethanol bath and lyophilized. No NMR signals from amylin wereNMR SpectroscopyUnless 1485-00-3 chemical information otherwise noted, a 600 MHz Varian Inova instrument equipped with a cryogenic probe was used for all NMR experiments. NMR assignments for 15N-amylin in 95 DMSO/ 5 DCA at a temperature of 25uC and pH* 3.5 were obtained from 3D TOCSY-HSQC (70 ms mix time) and 3D NOESYHSQC (250 ms mix time) experiments. Assignments have beenHydrogen Exchange in Amylin Fibrilsdeposited in the TA 02 manufacturer BioMagResBank (BMRB) under accession number 18795. Amide proton HX in the fibrils was read out from the lyophilized partially exchanged aliquots dissolved in 95 d6DMSO/5 d2-DCA using 2D 1H-15N HSQC spectra recorded at a temperature of 25uC. The d6-DMSO signal was used for the deuterium lock. The 2D 1H-15N HSQC spectra were collected with 1024 complex points in the 1H dimension and 32 complex points in the 15N dimension. Spectra were typically acquired with 16 transients averaged per free induction decay for a total acquisition time of 21 minutes. The NMR data were processed and 1H-15N crosspeak heights were measured using the iNMR software package (Mestrelab Research).shows amide proton intensity decay data for four representative residues. The amide proton of residue C2, which is in the unstructured N-terminus of amylin, exchanges with a fast rate. Residue G33, in strand b2 of the amylin fibril model exchanges with an intermediate rate. Amide protons that exchange with slow rates are represented by H18 and Y37, the C-terminal residues in strands b1 and b2. The observed differences in exchange rates between residues within the same strand (e.g. G33 and Y37 from strand b2), suggests that structural stability varies within a given element of secondary structure, as is often found in folded globular proteins [17,34].Gaussian Network Model Calculations using the ssNMR Model of Amylin FibrilsTwo models of the amylin fibril structure satisfy the ssNMR data: 4eql24930x2 and 4eql5432x2 [10]. The models differ with respect to the b-strand two-residue periodicity that determines which residues face the interior and exterior of the amylin bhairpin fold [10]. Except where noted, the 4eql5432x2 mode.Nditions for the qHX experiments. (1) To start, 0.1 mg lyophilized, un-fibrillized 15 N amylin was dissolved in 220 ml 95 DMSO/5 DCA at an apparent pH measured in DMSO (pH*) of 3.5, to give an amylin concentration of 0.12 mM. The heteronuclear single-quantum correlation (1H-15N HSQC) spectrum obtained at 25uC showed that amylin is soluble, monomeric, unfolded, and thus amenable to NMR spectroscopy. The spectrum showed no changes after 1 month at room temperature, demonstrating amylin is stable in 95 DMSO. 25033180 Additional pulse-field gradient translational diffusion NMR experiments [29] showed that amylin in DMSO has an ?apparent hydrodynamic radius of 1561 A, close to the expected ?value of 17 A for an unfolded monomer (Figure S1). (2) Next, it was determined that negligible amounts of 15N-amylin monomers remain in solution when amylin undergoes fibrillization, and that lyophillization does not disrupt the fibrils. A 0.12 mM 15N-amylin sample in H2O buffer containing 10 mM sodium phosphate pH 7.4 with 10 (v/v) acetonitrile was fibrillized without agitation for 4 days at 37uC. Electron microscopy (EM) images of fibrils grown under these conditions are shown in Figure S2. Amylin fibrils were sedimented at 15,000 g for 30 min. The supernatant, and pellet resuspended in H2O, were flash-frozen in a dry ice/ ethanol bath and lyophilized. No NMR signals from amylin wereNMR SpectroscopyUnless otherwise noted, a 600 MHz Varian Inova instrument equipped with a cryogenic probe was used for all NMR experiments. NMR assignments for 15N-amylin in 95 DMSO/ 5 DCA at a temperature of 25uC and pH* 3.5 were obtained from 3D TOCSY-HSQC (70 ms mix time) and 3D NOESYHSQC (250 ms mix time) experiments. Assignments have beenHydrogen Exchange in Amylin Fibrilsdeposited in the BioMagResBank (BMRB) under accession number 18795. Amide proton HX in the fibrils was read out from the lyophilized partially exchanged aliquots dissolved in 95 d6DMSO/5 d2-DCA using 2D 1H-15N HSQC spectra recorded at a temperature of 25uC. The d6-DMSO signal was used for the deuterium lock. The 2D 1H-15N HSQC spectra were collected with 1024 complex points in the 1H dimension and 32 complex points in the 15N dimension. Spectra were typically acquired with 16 transients averaged per free induction decay for a total acquisition time of 21 minutes. The NMR data were processed and 1H-15N crosspeak heights were measured using the iNMR software package (Mestrelab Research).shows amide proton intensity decay data for four representative residues. The amide proton of residue C2, which is in the unstructured N-terminus of amylin, exchanges with a fast rate. Residue G33, in strand b2 of the amylin fibril model exchanges with an intermediate rate. Amide protons that exchange with slow rates are represented by H18 and Y37, the C-terminal residues in strands b1 and b2. The observed differences in exchange rates between residues within the same strand (e.g. G33 and Y37 from strand b2), suggests that structural stability varies within a given element of secondary structure, as is often found in folded globular proteins [17,34].Gaussian Network Model Calculations using the ssNMR Model of Amylin FibrilsTwo models of the amylin fibril structure satisfy the ssNMR data: 4eql24930x2 and 4eql5432x2 [10]. The models differ with respect to the b-strand two-residue periodicity that determines which residues face the interior and exterior of the amylin bhairpin fold [10]. Except where noted, the 4eql5432x2 mode.
