We report here the identification of the key sites for the beta structure motifs of the islet amyloid polypeptide (IAPP) analogs by using scanning tunneling microscopy (STM). Duplex folding structures in human IAPP (hIAPP ) assembly were observed featuring a hairpin structure. The multiplicity in rIAPP assembly structures indicates the polydispersity of the rat IAPP 8-37 (rIAPP ) beta-like motifs. The bimodal length distribution of beta structure motifs for rIAPP R18H indicates the multiple beta segments linked by turns. The IAPP 8-37 analogs share common structure motifs of IAPP [8][9][10][11][12][13][14][15][16][17] with the most probable key sites at positions around Ser 19 ∕Ser 20 and Gly 24 . These observations reveal the similar amyloid formation tendency in the C and N terminus segments because of the sequence similarity, while the differences in specific amino acids at each key site manifest the effect of sequence variations. The results could be beneficial for studying structural polymorphism of amyloidal peptides with multiple beta structure motifs.amylin | folding sites | self-assembly | amyloid H uman islet amyloid polypeptide (hIAPP, amylin) is a major component in pancreatic amyloid deposits, which have been found in a majority of patients with type 2 diabetes (1-3). Human IAPP with 37 amino acid residues is known to form soluble aggregates that further assemble into protofibrils and mature fibrils and eventually develop into plagues (4, 5), and many studies have been conducted to identify the core regions with amyloidogenic properties (6-8). By using coordinated fiber X-ray diffraction (XRD) (9, 10), electron diffraction, and cryoelectron microscopy (10), the fibrillar structures of hIAPP have been identified as a beta-sheet structure with beta-strands perpendicular to the fiber axis, and the separation between neighboring strands is 4.7 Å. The parallel beta-structures of hIAPP have been proposed by using electron paramagnetic resonance spectroscopy of spinlabeled derivatives of hIAPP (11), and the "serpentine" model has been derived based on electron microscopy and scanning transmission electron microscopy data (12). Recent XRD studies have revealed a structural motif of short segments derived from a variety of amyloidal proteins (13-15). The atomic level structural model for hIAPP 21-27 revealed a pronounced bend facilitated by Gly 24 , and the model of hIAPP based on the crystalline structures of hIAPP 21-27 and hIAPP 28-33 segments indicated the beta-spine steric zipper structure for hIAPP 23-37 (two beta-sheets with interdigitated side chains) (15). The beta-hairpin structure of hIAPP has also been obtained by solid-state nuclear magnetic resonance (NMR) (16), suggesting the parallel beta-sheet structures with 10 residues in the core domains. The fragment IAPP 1-7 is believed to be non-beta-sheet structure (17) as the result of the disulfide bond between cysteine residues 2 and 7.As an important analog of IAPP, rat islet amyloid polypeptide (rIAPP) is reported to form no fibrils in soluti...

Regulatory T-cells (Tregs) are generally regarded as key immunomodulators that maintain immune tolerance and counteract tissue damage in a variety of immune-mediated disorders. However, its role in myocardial ischaemia/reperfusion injury (MIRI) remains unknown. The purpose of the present study was to determine whether Tregs exert a beneficial effect on mouse MIRI. We examined the role of Tregs in murine MIRI by depletion using 'depletion of regulatory T-cell' (DEREG) mice and adoptive transfer using Forkhead box P3 (Foxp3)-GFP knockin mice and the mechanisms of cardio protection were further studied in vivo and in vitro. Tregs rapidly accumulated in murine hearts following MIRI. Selective depletion of Tregs in the DEREG mouse model resulted in aggravated MIRI. In contrast, the adoptive transfer of in vitro-activated Tregs suppressed MIRI, whereas freshly isolated Tregs had no effect. Mechanistically, activated Treg-mediated protection against MIRI was not abrogated by interleukin (IL)-10 or transforming growth factor (TGF)-β1 inhibition but was impaired by the genetic deletion of cluster of differentiation 39 (CD39). Moreover, adoptive transfer of in vitro-activated Tregs attenuated cardiomyocyte apoptosis, activated a pro-survival pathway involving Akt and extracellular-signal-regulated kinase (ERK) and inhibited neutrophil infiltration, which was compromised by CD39 deficiency. Finally, the peripheral blood mononuclear cells of acute myocardial infarction (AMI) patients after primary percutaneous coronary intervention (PCI) revealed a decrease in CD4+CD25+CD127low Tregs and a relative increase in CD39+ cells within the Treg population. In conclusion, our data validated a protective role for Tregs in MIRI. Moreover, in vitro-activated Tregs ameliorated MIRI via a CD39-dependent mechanism, representing a putative therapeutic strategy.