Identifying Structural Features of Fibrillar Islet Amyloid Polypeptide Using Site-directed Spin Labeling

Pancreatic amyloid deposits, composed primarily of the 37-residue islet amyloid polypeptide (IAPP), are a characteristic feature found in more than 90% of patients with type II diabetes. Although IAPP amyloid deposits are associated with areas of pancreatic islet β-cell dysfunction and depletion and are thought to play a role in disease, their structure is unknown. We used electron paramagnetic resonance spectroscopy to analyze eight spin-labeled derivatives of IAPP in an effort to determine structural features of the peptide. In solution, all eight derivatives gave rise to electron paramagnetic resonance spectra with sharp lines indicative of rapid motion on the sub-nanosecond time scale. These spectra are consistent with a rapidly tumbling and highly dynamic peptide. In contrast, spectra for the fibrillar form exhibit reduced mobility and the presence of strong intermolecular spin-spin interactions. The latter implies that the peptide subunits are ordered and that the same residues from neighboring peptides are in close proximity to one another. Our data are consistent with a parallel arrangement of IAPP peptides within the amyloid fibril. Analysis of spin label mobility indicates a high degree of order throughout the peptide, although the N-terminal region is slightly less ordered. Possible similarities with respect to the domain organization and parallelism of Alzheimer's amyloid β peptide fibrils are discussed. Pancreatic amyloid deposits, composed primarily of the 37-residue islet amyloid polypeptide (IAPP), are a characteristic feature found in more than 90% of patients with type II diabetes. Although IAPP amyloid deposits are associated with areas of pancreatic islet β-cell dysfunction and depletion and are thought to play a role in disease, their structure is unknown. We used electron paramagnetic resonance spectroscopy to analyze eight spin-labeled derivatives of IAPP in an effort to determine structural features of the peptide. In solution, all eight derivatives gave rise to electron paramagnetic resonance spectra with sharp lines indicative of rapid motion on the sub-nanosecond time scale. These spectra are consistent with a rapidly tumbling and highly dynamic peptide. In contrast, spectra for the fibrillar form exhibit reduced mobility and the presence of strong intermolecular spin-spin interactions. The latter implies that the peptide subunits are ordered and that the same residues from neighboring peptides are in close proximity to one another. Our data are consistent with a parallel arrangement of IAPP peptides within the amyloid fibril. Analysis of spin label mobility indicates a high degree of order throughout the peptide, although the N-terminal region is slightly less ordered. Possible similarities with respect to the domain organization and parallelism of Alzheimer's amyloid β peptide fibrils are discussed. Pancreatic amyloid deposits have been identified as a hallmark of non-insulin-dependent (type II) diabetes mellitus. More than 90% of patients with type II diabetes exhibit amyloid deposits in areas of β-cell dysfunction and death (1Kahn S.E. Andrikopoulos S. Verchere C.B. Diabetes. 1999; 48: 241-253Crossref PubMed Scopus (424) Google Scholar, 2de Koning E.J. Bodkin N.L. Hansen B.C. Clark A. Diabetologia. 1993; 36: 378-384Crossref PubMed Scopus (154) Google Scholar). The major component of these deposits is the 37-residue islet amyloid polypeptide (IAPP) 1The abbreviations used are: IAPP, islet amyloid polypeptide; EM, electron microscopy; CD, circular dichroism; ThT, thioflavin T; NMR, nuclear magnetic resonance; EPR, electron paramagnetic resonance; SDSL, site-directed spin labeling; Aβ, amyloid β; HFIP, hexafluoroisopropanol; MTSL, 1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl methanethiosulfonate.1The abbreviations used are: IAPP, islet amyloid polypeptide; EM, electron microscopy; CD, circular dichroism; ThT, thioflavin T; NMR, nuclear magnetic resonance; EPR, electron paramagnetic resonance; SDSL, site-directed spin labeling; Aβ, amyloid β; HFIP, hexafluoroisopropanol; MTSL, 1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl methanethiosulfonate. (3Westermark P. Wernstedt C. O'Brien T.D. Hayden D.W. Johnson K.H. Am. J. Pathol. 1987; 127: 414-417PubMed Google Scholar, 4Cooper G.J. Willis A.C. Clark A. Turner R.C. Sim R.B. Reid K.B. Proc. Natl. Acad. Sci. U. S. A. 1987; 84: 8628-8632Crossref PubMed Scopus (1166) Google Scholar), and multiple lines of investigation have provided experimental evidence implicating human IAPP amyloid deposits in type II diabetes (5Janson J. Soeller W.C. Roche P.C. Nelson R.T. Torchia A.J. Kreutter D.K. Butler P.C. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 7283-7288Crossref PubMed Scopus (301) Google Scholar, 6de Koning E.J. Morris E.R. Hofhuis F.M. Posthuma G. Hèoppener J.W. Morris J.F. Capel P.J. Clark A. Verbeek J.S. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 8467-8471Crossref PubMed Scopus (93) Google Scholar, 7MacArthur D.L. de Koning E.J. Verbeek J.S. Morris J.F. Clark A. Diabetologia. 1999; 42: 1219-1227Crossref PubMed Scopus (35) Google Scholar, 8O'Brien T.D. Butler P.C. Kreutter D.K. Kane L.A. Eberhardt N.L. Am. J. Pathol. 1995; 147: 609-616PubMed Google Scholar). Although pancreatic amyloid deposits in a diabetic patient were first identified more than a century ago, structural features of these deposits were not described until recently. Electron microscopy (EM) studies of IAPP deposits revealed the presence of long fibrillar structures (9Westermark P. Li Z.C. Westermark G.T. Leckstrèom A. Steiner D.F. FEBS Lett. 1996; 379: 203-206Crossref PubMed Scopus (162) Google Scholar, 10Goldsbury C.S. Cooper G.J. Goldie K.N. Mèuller S.A. Saafi E.L. Gruijters W.T. Misur M.P. Engel A. Aebi U. Kistler J. J. Struct. Biol. 1997; 119: 17-27Crossref PubMed Scopus (256) Google Scholar, 11Goldsbury C. Goldie K. Pellaud J. Seelig J. Frey P. Mèuller S.A. Kistler J. Cooper G.J. Aebi U. J. Struct. Biol. 2000; 130: 352-362Crossref PubMed Scopus (288) Google Scholar). Fourier transform infrared and circular dichroism (CD) analysis of IAPP fibrils made from full-length as well as shorter fragments indicates the presence of significant amounts of β-sheet structure in the fibrillar form (12Higham C.E. Jaikaran E.T. Fraser P.E. Gross M. Clark A. FEBS Lett. 2000; 470: 55-60Crossref PubMed Scopus (108) Google Scholar, 13Kayed R. Bernhagen J. Greenfield N. Sweimeh K. Brunner H. Voelter W. Kapurniotu A. J. Mol. Biol. 1999; 287: 781-796Crossref PubMed Scopus (314) Google Scholar). X-ray and electron diffraction studies using aligned fibrils have shown that the peptide chains are arranged in a cross-β-conformation with the individual β-strands perpendicular to the fibril axis (14Sumner Makin O. Serpell L.C. J. Mol. Biol. 2004; 335: 1279-1288Crossref PubMed Scopus (130) Google Scholar, 15Jaikaran E.T. Higham C.E. Serpell L.C. Zurdo J. Gross M. Clark A. Fraser P.E. J. Mol. Biol. 2001; 308: 515-525Crossref PubMed Scopus (215) Google Scholar). Beyond these observations, little is known about the molecular details of IAPP in the fibrillar form. Amyloid deposits have been identified in a number of human diseases, such as Alzheimer's disease, Parkinson's disease, and familial amyloidotic polyneuropathy (16Soto C. Nat. Rev. Neurosci. 2003; 4: 49-60Crossref PubMed Scopus (1084) Google Scholar). Although the primary structure of amyloid forming proteins varies widely, most amyloid deposits appear to share common characteristics, such as the cross-β-structure, and the ability to bind thioflavin T (ThT) and Congo red (17Sunde M. Serpell L.C. Bartlam M. Fraser P.E. Pepys M.B. Blake C.C. J. Mol. Biol. 1997; 273: 729-739Crossref PubMed Scopus (1409) Google Scholar). Because of the non-crystalline and insoluble nature of amyloid deposits, it has been difficult to obtain a detailed molecular structure of amyloidogenic proteins in the fibrillar form using conventional biophysical techniques such as x-ray crystallography and solution-state nuclear magnetic resonance (NMR) spectroscopy. In contrast, other magnetic resonance techniques, such as solid-state NMR (18Griffiths J.M. Ashburn T.T. Auger M. Costa P.R. Griffin R.G. J. Am. Chem. Soc. 1995; 117: 3539-3546Crossref Scopus (128) Google Scholar, 19Tycko R. Curr. Opin. Chem. Biol. 2000; 4: 500-506Crossref PubMed Scopus (86) Google Scholar, 20Petkova A.T. Ishii Y. Balbach J.J. Antzutkin O.N. Leapman R.D. Delaglio F. Tycko R. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 16742-16747Crossref PubMed Scopus (1635) Google Scholar) and electron paramagnetic resonance (EPR) spectroscopy together with site-directed spin labeling (SDSL) (21Margittai M. Langen R. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 10278-10283Crossref PubMed Scopus (239) Google Scholar, 22Der-Sarkissian A. Jao C.C. Chen J. Langen R. J. Biol. Chem. 2003; 278: 37530-37535Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar, 23Torok M. Milton S. Kayed R. Wu P. McIntire T. Glabe C.G. Langen R. J. Biol. Chem. 2002; 277: 40810-40815Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar, 24Serag A.A. Altenbach C. Gingery M. Hubbell W.L. Yeates T.O. Biochemistry. 2001; 40: 9089-9096Crossref PubMed Scopus (67) Google Scholar) have been used successfully to obtain structural and dynamic features of amyloidogenic proteins in their fibrillar form (for review, see Ref. 25Tycko R. Curr. Opin. Struct. Biol. 2004; 14: 96-103Crossref PubMed Scopus (350) Google Scholar). In the present study, we used EPR spectroscopy in combination with SDSL to obtain structural features of full-length IAPP. In SDSL, a cysteine-specific nitroxide spin label is introduced at selected sites of the protein molecule, resulting in a nitroxide-labeled side chain (R1, see Fig. 1). EPR spectra of these R1 reporter groups reflect the local environment of the label and can be used to classify a given site as a loop region, as an exposed or buried site, or as a tertiary contact site (26McHaourab H.S. Lietzow M.A. Hideg K. Hubbell W.L. Biochemistry. 1996; 35: 7692-7704Crossref PubMed Scopus (527) Google Scholar, 27Margittai M. Fasshauer D. Pabst S. Jahn R. Langen R. J. Biol. Chem. 2001; 276: 13169-13177Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar, 28Isas J.M. Langen R. Haigler H.T. Hubbell W.L. Biochemistry. 2002; 41: 1464-1473Crossref PubMed Scopus (100) Google Scholar). Furthermore, the distance between two R1 side chains can be estimated from EPR spectra, given the presence of spin-spin interactions between spin labels (29Hubbell W.L. Cafiso D.S. Altenbach C. Nat. Struct. Biol. 2000; 7: 735-739Crossref PubMed Scopus (718) Google Scholar). We find that most regions of IAPP in its fibrillar form are arranged in a highly ordered fashion with the same residues from different strands in close proximity to one another, indicating a parallel arrangement of IAPP peptides within the fibril. The organization of IAPP in the fibrillar form is similar to that observed for Alzheimer's Aβ peptide fibrils obtained using EPR/SDSL (23Torok M. Milton S. Kayed R. Wu P. McIntire T. Glabe C.G. Langen R. J. Biol. Chem. 2002; 277: 40810-40815Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar) and NMR (20Petkova A.T. Ishii Y. Balbach J.J. Antzutkin O.N. Leapman R.D. Delaglio F. Tycko R. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 16742-16747Crossref PubMed Scopus (1635) Google Scholar) spectroscopy. These similarities suggest that the molecular architecture of IAPP and Aβ fibrils could be related. Chemicals and Peptides—Hexafluoroisopropanol (HFIP) and ThT were obtained from Sigma-Aldrich. Synthetic wild-type human IAPP was obtained from Bachem (King of Prussia, PA). The spin label, 1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl methanethiosulfonate (MTSL), was obtained from Toronto Research Chemicals (Toronto, Canada). The thiol-reactive pyrene label, N-(1-pyrenyl)maleimide, was obtained from Molecular Probes of IAPP residues the were was using on an peptide of full-length IAPP on were from peptides were high and were for molecular peptides were and at until spin peptides were with of for at was high and spin-labeled peptides were for molecular using of peptide found to of IAPP Biochemistry. 2002; 41: PubMed Scopus Google Scholar). peptides were in and a spin with the was with and the peptide was using were at in using an of for the wild-type peptide Biochemistry. 2002; 41: PubMed Scopus Google Scholar) and for the peptide on an of for PubMed Scopus Google in were at of peptide in were and the was using a The peptide was in was to at for a of the of the fibrils were from and with of IAPP in were with the of wild-type IAPP or IAPP in HFIP, and fibrils as described EPR EPR fibril were were obtained on a with an EPR spectra were obtained at using a of or at an of with a of were to the same number of using the and are of peptide in were with of in and The peptide was in to to and a of IAPP fibril in were obtained from fibrils from IAPP as described spectra were obtained using a were at a of with an time of were between spectra were using for the ThT were as described for spectroscopy. ThT was and were at with at were at with and of and spectra of IAPP fibrils were obtained with at a of and and of and spectra of IAPP were using the at were using a Electron of fibrillar IAPP was was on were with of for and with of was for with for two residues that can form a J. Cooper G.J. Reid Am. J. PubMed Google Scholar). is not the is present in the fibrillar it is for fibril in Synthetic peptides the N-terminal residues of IAPP have been found to form amyloid fibrils with a similar to that of the full-length peptide C. Goldie K. Pellaud J. Seelig J. Frey P. Mèuller S.A. Kistler J. Cooper G.J. Aebi U. J. Struct. Biol. 2000; 130: 352-362Crossref PubMed Scopus (288) Google Scholar), implies that the two are not for the of amyloid fibrils in determine fibril full-length IAPP the two we used and ThT were in wild-type and IAPP spectra and with at These spectra are characteristic of an structural associated with fibril spectra were from fibrillar wild-type and IAPP, we observed a of the at with a in the at fibril and These are indicative of a from an to a β-sheet structure and are in with data on IAPP (12Higham C.E. Jaikaran E.T. Fraser P.E. Gross M. Clark A. FEBS Lett. 2000; 470: 55-60Crossref PubMed Scopus (108) Google Scholar, 13Kayed R. Bernhagen J. Greenfield N. Sweimeh K. Brunner H. Voelter W. Kapurniotu A. J. Mol. Biol. 1999; 287: 781-796Crossref PubMed Scopus (314) Google Scholar). The ability of wild-type and IAPP to form fibrillar structures was using ThT, a known to bind to amyloid fibrils C. Butler P.C. Eberhardt N.L. J. PubMed Scopus Google Scholar, H. K. M. T. PubMed Scopus Google Scholar). fibril ThT at was at different time wild-type and IAPP, we observed in ThT similar to Biochemistry. 2002; 41: PubMed Scopus Google Scholar). In the observed in ThT the of fibrils with highly similar not Although the in is close to the of the ThT it is that the N-terminal of IAPP could to the of fibril E.T. Higham C.E. Serpell L.C. Zurdo J. Gross M. Clark A. Fraser P.E. J. Mol. Biol. 2001; 308: 515-525Crossref PubMed Scopus (215) Google Scholar). we used to the of the two the fibril We observed similar fibril for the wild-type and peptides and together with and ThT these similarities that the of the two residues not the ability of full-length IAPP to form amyloid EPR of and of IAPP obtain the molecular architecture of IAPP in their and fibrillar we eight of IAPP were at selected sites throughout the to structural from different regions of the peptide. We found that IAPP in gave rise to EPR spectra with sharp lines with a as in Fig. for the These features are characteristic of highly R1 label with a time in the sub-nanosecond time in with the structure In to the fibrillar IAPP gave rise to and red in the fibrillar is at These features for IAPP fibrils in from R1 labels spin-spin interactions a in EPR of IAPP with for the presence of spin-spin interactions in the spectra obtained for fibrils from IAPP we spin fibrils were from a of and IAPP. The for these is as and IAPP in the the of an R1 label on a given IAPP close proximity to label on a neighboring be reduced with amounts of IAPP. spin-spin interactions and in rise to EPR spectra with reduced and lines that are as with spectra from obtained from the IAPP with amounts of wild-type IAPP and the are shown in Fig. and C. from reduced and EPR lines as with the obtained in the of indicates the presence of significant spin-spin in the form. In of spin indicates that the and peptides can and form fibrils fibrils from these have a similar to that obtained for fibrils from wild-type IAPP data not These data suggest that the R1 label is well within the and that the and peptides can similar fibrillar we obtained EPR spectra for fibrils from and an to wild-type IAPP peptide of from all eight of IAPP spectra obtained from were and were of indicating the presence of spin-spin interactions. In contrast, spectra of at all eight sites indicating the of intermolecular spin-spin interactions and close proximity of sites from neighboring the close proximity of sites using an we a of IAPP. Fig. the spectra for IAPP with pyrene at the in the form in and the of fibrillar In the of the fibrillar we observed a at characteristic of pyrene was not observed in IAPP. are from the of two that are in contact and the of pyrene in fibrillar IAPP indicates the close proximity of pyrene from neighboring IAPP peptides and is in with the of EPR EPR of obtain details on the molecular structure of IAPP, we the mobility of R1 in the fibrillar form. Our spin that spin-spin interactions to the and observed in the fibrillar In the of spin-spin EPR on the of high with peptide, the EPR spectra from fibrillar IAPP are primarily R1 shown in Fig. all spectra between the EPR lines and lines with spectra, indicating the of R1 at all eight in to sites on neighboring in close proximity to one another, site more ordered fibril was most at sites in the region of IAPP between residues less was observed for sites in the of the peptide as the and the slightly less lines for sites and more of mobility of the R1 label can be obtained using the The N-terminal residues and of and sites between residues from to that the two N-terminal sites less than sites within the of the peptide. Our was to the structural organization of IAPP in its fibrillar form. EPR and SDSL, we found that IAPP a from a highly dynamic structure in to a and parallel structure in the fibril. Although the mobility of all eight sites was reduced in the fibrillar we observed in R1 mobility that structural regions within IAPP. We found that the region of IAPP and the of with of the presence of spin-spin interactions within region, of mobility that these residues are within the of the IAPP fibril. with of IAPP fragments that residues are not for fibril E.T. Higham C.E. Serpell L.C. Zurdo J. Gross M. Clark A. Fraser P.E. J. Mol. Biol. 2001; 308: 515-525Crossref PubMed Scopus (215) Google Scholar, P. U. Johnson K.H. Westermark G.T. C. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, J. Mol. Biol. 1999; PubMed Scopus Google Scholar). We have observed that in to a in mobility was the presence of spin at all eight that the R1 label on site of a given peptide is in close proximity to the same site on neighboring is of pyrene that the pyrene from neighboring peptides to be within In a SDSL of fibrils from EPR spectra structure two were observed (21Margittai M. Langen R. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 10278-10283Crossref PubMed Scopus (239) Google Scholar). of the from spin labels on the EPR time an of R1 labels within the fibril. We observed reduced structure of for sites within the region, although not as as in the of we the presence of spin and contact between R1 labels from neighboring for these is difficult to determine the of present in the presence of spin could be an we used to determine the of the these we found that the from spin could be high at all sites within the region and to for and not the presence of spin at all eight sites in IAPP, with the of pyrene indicates a parallel arrangement of strands within the fibril. The present data on IAPP are similar to obtained from for the Alzheimer's Aβ peptide (23Torok M. Milton S. Kayed R. Wu P. McIntire T. Glabe C.G. Langen R. J. Biol. Chem. 2002; 277: 40810-40815Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar). In the of Aβ, we observed spin-spin interactions and EPR spectra with observed The EPR together with solid-state NMR studies H. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, O.N. Balbach J.J. Leapman R.D. J. Tycko R. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar, J.J. A.T. Antzutkin O.N. Tycko R. J. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar), a arrangement of individual strands for given the between EPR data and that of Aβ, it is highly that a similar parallel structure to IAPP. In a parallel arrangement be more common for with such as IAPP, Aβ (23Torok M. Milton S. Kayed R. Wu P. McIntire T. Glabe C.G. Langen R. J. Biol. Chem. 2002; 277: 40810-40815Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar), A. Jao C.C. Chen J. Langen R. J. Biol. Chem. 2003; 278: 37530-37535Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar), (21Margittai M. Langen R. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 10278-10283Crossref PubMed Scopus (239) Google Scholar), and as for the U. R.B. A.C. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: PubMed Scopus Google Scholar). shorter and peptide fragments of Aβ Costa P.R. J.M. E.J. Auger M. Ashburn T.T. R.G. Griffin R.G. Nat. Struct. Biol. 1995; PubMed Scopus Google Scholar, J.J. Ishii Y. Antzutkin O.N. Leapman R.D. F. J. Tycko R. Biochemistry. 2000; PubMed Scopus Google Scholar, A.T. G. F. Leapman R.D. Tycko R. J. Mol. Biol. 2004; 335: PubMed Scopus Google Scholar) and IAPP (18Griffiths J.M. Ashburn T.T. Auger M. Costa P.R. Griffin R.G. J. Am. Chem. Soc. 1995; 117: 3539-3546Crossref Scopus (128) Google Scholar, T.T. Auger M. J. Am. Chem. Soc. Scopus Google Scholar), β-sheet have been the role of in the organization of amyloid fibrils has been described Balbach J.J. Tycko R. J. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). In the is the residues are found the N-terminal of the peptide. Balbach J.J. Tycko R. J. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar) that of is for its parallel arrangement within a of the arrangement of shorter fragments of Although studies have not been for IAPP, of the to the that play a role in the organization of IAPP within In full-length IAPP, the N-terminal is all residues of IAPP. In contrast, the of the peptide of are found within the a of and residues an to IAPP that the parallel arrangement of full-length peptides within The similarities between IAPP and Aβ could to the organization of their given the similarities observed between the primary of IAPP and Aβ peptides Westermark P. R. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar) found a the region was to residues or the region, of Furthermore, found that Aβ fibrils can as for IAPP not the Westermark P. R. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar), that at IAPP could a structure similar to that of Aβ (20Petkova A.T. Ishii Y. Balbach J.J. Antzutkin O.N. Leapman R.D. Delaglio F. Tycko R. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 16742-16747Crossref PubMed Scopus (1635) Google Scholar, Y. R. J. Mol. Biol. 2004; 335: PubMed Scopus Google Scholar) in the fibrillar form. Aβ a ordered region that spin-spin interactions. The N-terminal region of Aβ is of order and that the of the the two IAPP N-terminal and we observed with of and a order for these Although we have not site in the these two at are close to obtained for similar sites from the of Aβ (23Torok M. Milton S. Kayed R. Wu P. McIntire T. Glabe C.G. Langen R. J. Biol. Chem. 2002; 277: 40810-40815Abstract Full Text Full Text PDF PubMed Scopus (340) Google Scholar), indicating the that the of IAPP is not within the most highly ordered Furthermore, we find that the N-terminal are not for fibril and that the and wild-type peptides with IAPP, that all of the peptide can similar fibrillar the between residues and wild-type IAPP fibril in it that the N-terminal region the of a β-sheet In EPR/SDSL data have to structural features of IAPP in the fibrillar form. Our EPR data are consistent with a IAPP fibrils are from the ordered parallel arrangement of IAPP we have been to structural regions of IAPP EPR/SDSL studies to structural features of IAPP such as or regions J. Mol. Biol. 2001; 308: PubMed Scopus Google Scholar), and to experimental to a of IAPP in the fibrillar form. We and for and for its

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