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1. α-CGRP disrupts amylin fibrillization and regulates insulin secretion: implications on diabetes and migraine

   https://doi.org/10.1039/D1SC01167G  

   Gray, Amber L.; Antevska, Aleksandra; Link, Benjamin A.; Bogin, Bryan; Burke, Susan J.; Dupuy, Samuel D.; Collier, J. Jason; Levine, Zachary A.; Karlstad, Michael D.; Do, Thanh D. (April 2021, Chemical Science)

   Despite being relatively benign and not an indicative signature of toxicity, fibril formation and fibrillar structures continue to be key factors in assessing the structure–function relationship in protein aggregation diseases. The inability to capture molecular cross-talk among key players at the tissue level before fibril formation greatly accounts for the missing link toward the development of an efficacious therapeutic intervention for Type II diabetes mellitus (T2DM). We show that human α-calcitonin gene-related peptide (α-CGRP) remodeled amylin fibrillization. Furthermore, while CGRP and/or amylin monomers reduce the secretion of both mouse Ins1 and Ins2 proteins, CGRP oligomers have a reverse effect on Ins1. Genetically reduced Ins2, the orthologous version of human insulin, has been shown to enhance insulin sensitivity and extend the life-span in old female mice. Beyond the mechanistic insights, our data suggest that CGRP regulates insulin secretion and lowers the risk of T2DM. Our result rationalizes how migraine might be protective against T2DM. We envision the new paradigm of CGRP : amylin interactions as a pivotal aspect for T2DM diagnostics and therapeutics. Maintaining a low level of amylin while increasing the level of CGRP could become a viable approach toward T2DM prevention and treatment. 

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2. Critical Conditions Regulating the Gelation in Macroionic Cluster Solutions

   https://doi.org/10.1002/advs.202308902  

   Xu, Xiaohan; Yang, Yuqing; Zhou, Yifan; Xiao, Kexing; Szymanowski, Jennifer_E_S; Sigmon, Ginger_E; Burns, Peter_C; Liu, Tianbo (March 2024, Advanced Science)

   Abstract The critical gelation conditions observed in dilute aqueous solutions of multiple nanoscale uranyl peroxide molecular clusters are reported, in the presence of multivalent cations. This gelation is dominantly driven by counterion‐mediated attraction. The gelation areas in the corresponding phase diagrams all appear in similar locations, with a characteristic triangle shape outlining three critical boundary conditions, corresponding to the critical cluster concentration, cation/cluster ratio, and the degree of counterion association with increasing cluster concentration. These interesting phrasal observations reveal general conditions for gelation driven by electrostatic interactions in hydrophilic macroionic solutions. 

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3. Thermodynamic phase diagram of amyloid-β (16–22) peptide

   https://doi.org/10.1073/pnas.1819592116  

   Wang, Yiming; Bunce, Samuel J.; Radford, Sheena E.; Wilson, Andrew J.; Auer, Stefan; Hall, Carol K. (February 2019, Proceedings of the National Academy of Sciences)

   The aggregation of monomeric amyloid β protein (Aβ) peptide into oligomers and amyloid fibrils in the mammalian brain is associated with Alzheimer’s disease. Insight into the thermodynamic stability of the Aβ peptide in different polymeric states is fundamental to defining and predicting the aggregation process. Experimental determination of Aβ thermodynamic behavior is challenging due to the transient nature of Aβ oligomers and the low peptide solubility. Furthermore, quantitative calculation of a thermodynamic phase diagram for a specific peptide requires extremely long computational times. Here, using a coarse-grained protein model, molecular dynamics (MD) simulations are performed to determine an equilibrium concentration and temperature phase diagram for the amyloidogenic peptide fragment Aβ_16–22. Our results reveal that the only thermodynamically stable phases are the solution phase and the macroscopic fibrillar phase, and that there also exists a hierarchy of metastable phases. The boundary line between the solution phase and fibril phase is found by calculating the temperature-dependent solubility of a macroscopic Aβ_16–22fibril consisting of an infinite number of β-sheet layers. This in silico determination of an equilibrium (solubility) phase diagram for a real amyloid-forming peptide, Aβ_16–22, over the temperature range of 277–330 K agrees well with fibrillation experiments and transmission electron microscopy (TEM) measurements of the fibril morphologies formed. This in silico approach of predicting peptide solubility is also potentially useful for optimizing biopharmaceutical production and manufacturing nanofiber scaffolds for tissue engineering. 

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4. Mesoscopic protein-rich clusters host the nucleation of mutant p53 amyloid fibrils

   https://doi.org/10.1073/pnas.2015618118  

   Yang, David S.; Saeedi, Arash; Davtyan, Aram; Fathi, Mohsen; Sherman, Michael B.; Safari, Mohammad S.; Klindziuk, Alena; Barton, Michelle C.; Varadarajan, Navin; Kolomeisky, Anatoly B.; et al (March 2021, Proceedings of the National Academy of Sciences)

   The protein p53 is a crucial tumor suppressor, often called “the guardian of the genome”; however, mutations transform p53 into a powerful cancer promoter. The oncogenic capacity of mutant p53 has been ascribed to enhanced propensity to fibrillize and recruit other cancer fighting proteins in the fibrils, yet the pathways of fibril nucleation and growth remain obscure. Here, we combine immunofluorescence three-dimensional confocal microscopy of human breast cancer cells with light scattering and transmission electron microscopy of solutions of the purified protein and molecular simulations to illuminate the mechanisms of phase transformations across multiple length scales, from cellular to molecular. We report that the p53 mutant R248Q (R, arginine; Q, glutamine) forms, both in cancer cells and in solutions, a condensate with unique properties, mesoscopic protein-rich clusters. The clusters dramatically diverge from other protein condensates. The cluster sizes are decoupled from the total cluster population volume and independent of the p53 concentration and the solution concentration at equilibrium with the clusters varies. We demonstrate that the clusters carry out a crucial biological function: they host and facilitate the nucleation of amyloid fibrils. We demonstrate that the p53 clusters are driven by structural destabilization of the core domain and not by interactions of its extensive unstructured region, in contradistinction to the dense liquids typical of disordered and partially disordered proteins. Two-step nucleation of mutant p53 amyloids suggests means to control fibrillization and the associated pathologies through modifying the cluster characteristics. Our findings exemplify interactions between distinct protein phases that activate complex physicochemical mechanisms operating in biological systems. 

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5. Frustrated peptide chains at the fibril tip control the kinetics of growth of amyloid-β fibrils

   https://doi.org/10.1073/pnas.2110995118  

   Xu, Yuechuan; Knapp, Kaitlin; Le, Kyle N.; Schafer, Nicholas P.; Safari, Mohammad S.; Davtyan, Aram; Wolynes, Peter G.; Vekilov, Peter G. (September 2021, Proceedings of the National Academy of Sciences)

   Amyloid fibrillization is an exceedingly complex process in which incoming peptide chains bind to the fibril while concertedly folding. The coupling between folding and binding is not fully understood. We explore the molecular pathways of association of Aβ40 monomers to fibril tips by combining time-resolved in situ scanning probe microscopy with molecular modeling. The comparison between experimental and simulation results shows that a complex supported by nonnative contacts is present in the equilibrium structure of the fibril tip and impedes fibril growth in a supersaturated solution. The unraveling of this frustrated state determines the rate of fibril growth. The kinetics of growth of freshly cut fibrils, in which the bulk fibril structure persists at the tip, complemented by molecular simulations, indicate that this frustrated complex comprises three or four monomers in nonnative conformations and likely is contained on the top of a single stack of peptide chains in the fibril structure. This pathway of fibril growth strongly deviates from the common view that the conformational transformation of each captured peptide chain is templated by the previously arrived peptide. The insights into the ensemble structure of the frustrated complex may guide the search for suppressors of Aβ fibrillization. The uncovered dynamics of coupled structuring and assembly during fibril growth are more complex than during the folding of most globular proteins, as they involve the collective motions of several peptide chains that are not guided by a funneled energy landscape. 

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