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The naturally occurring nucleotide 2-deoxy-adenosine 5'-triphosphate (dATP) can be used by cardiac muscle as an alternative energy substrate for myosin chemomechanical activity. We and others have previously shown that dATP increases contractile force in normal hearts and models of depressed systolic function, but the structural basis of these effects has remained unresolved. In this work, we combine multiple techniques to provide structural and functional information at the angstrom-nanometer and millisecond time scales, demonstrating the ability to make both structural measurements and quantitative kinetic estimates of weak actin-myosin interactions that underpin sarcomere dynamics. Exploiting dATP as a molecular probe, we assess how small changes in myosin structure translate to electrostatic-based changes in sarcomere function to augment contractility in cardiac muscle. Through Brownian dynamics simulation and computational structural analysis, we found that deoxy-hydrolysis products [2-deoxy-adenosine 5'-diphosphate (dADP) and inorganic phosphate (Pi)] bound to prepowerstroke myosin induce an allosteric restructuring of the actin-binding surface on myosin to increase the rate of cross-bridge formation. We then show experimentally that this predicted effect translates into increased electrostatic interactions between actin and cardiac myosin in vitro. Finally, using small-angle X-ray diffraction analysis of sarcomere structure, we demonstrate that the proposed increased electrostatic affinity of myosin for actin causes a disruption of the resting conformation of myosin motors, resulting in their repositioning toward the thin filament before activation. The dATP-mediated structural alterations in myosin reported here may provide insight into an improved criterion for the design or selection of small molecules to be developed as therapeutic agents to treat systolic dysfunction.

Uropathogenic Escherichia coli account for the largest proportion of nosocomial infections in the United States. Nosocomial infections are a major source of increased costs and treatment complications. Many infections are biofilm associated, rendering antibiotic treatments ineffective or cause additional complications (e.g., microbiome depletion). This work presents a potentially complementary non-antibiotic strategy to fight nosocomial infections by inhibiting the formation of amyloid fibrils, a proteinaceous structural reinforcement known as curli in E. coli biofilms. Despite extensive characterization of the fibrils themselves and their associated secretion system, mechanistic details of curli assembly in vivo remain unclear. We hypothesized that, like other amyloid fibrils, curli polymerization involves a unique secondary structure termed "α-sheet". Biophysical studies herein confirmed the presence of α-sheet structure in prefibrillar species of CsgA, the major component of curli, as it aggregated. Binding of synthetic α-sheet peptides to the soluble α-sheet prefibrillar species inhibited CsgA aggregation in vitro and suppressed amyloid fibril formation in biofilms. Application of synthetic α-sheet peptides also enhanced antibiotic susceptibility and dispersed biofilm-resident bacteria for improved uptake by phagocytic cells. The ability of synthetic α-sheet peptides to reduce biofilm formation, improve antibiotic susceptibility, and enhance clearance by macrophages has broad implications for combating biofilm-associated infections. [ABSTRACT FROM AUTHOR]

All currently known structures of proteins together define ‘protein fold space’. To increase the general understanding of protein dynamics and protein folding, we selected a set of 807 proteins and protein domains that represent 95% of the currently known autonomous folded domains present in globular proteins. Native state and unfolding simulations of these representatives are now complete and accessible via a novel database containing over 11 000 simulations. Because protein folding is a microscopically reversible process, these simulations effectively sample protein folding across all of protein fold space. Here, we give an overview of how the representative proteins were selected and how the simulations were performed and validated. We then provide examples of different types of analyses that can be performed across our large set of simulations, made possible by the database approach. We further show how the unfolding simulations can be used to compare unfolding of structural elements in isolation and in different structural contexts, using as an example a short, triple stranded β-sheet that forms the WW domain and is present in several larger unrelated proteins.

Transthyretin, [[beta].sub.2]-microglobulin, lysozyme, and the prion protein are four of the best-characterized proteins implicated in amyloid disease. Upon partial acid denaturation, these proteins undergo conformational change into an amyloidogenic intermediate that can self-assemble into amyloid fibrils. Many experiments have shown that pH-mediated changes in structure are required for the formation of the amyloidogeneic intermediate, but it has proved impossible to characterize these conformational changes at high resolution using experimental means. To probe these conformational changes at atomic resolution, we have performed molecular dynamics simulations of these proteins at neutral and low pH. In low-pH simulations of all four proteins, we observe the formation of [alpha]-pleated sheet secondary structure, which was first proposed by L. Pauling and R. B. Corey [(1951) Proc. Natl. Acad. Sci. USA 37, 251-256]. In all [beta]-sheet proteins, transthyretin and [[beta].sub.2]-microglobulin, [alpha]-pleated sheet structure formed over the strands that are highly protected in hydrogen-exchange experiments probing amyloidogenic conditions. In lysozyme and the prion protein, [alpha]-sheets formed in the specific regions of the protein implicated in the amyloidogenic conversion. We propose that the formation of [alpha]-pleated sheet structure may be a common conformational transition in amyloidosis.

Here, we describe the folding/unfolding kinetics of [[alpha].sub.3]D, a small designed three-helix bundle. Both IR temperature jump and ultrafast fluorescence mixing methods reveal a single-exponential process consistent with a minimal folding time of 3.2 [+ or -] 1.2 [micro]s (at [approximately equal to] 50[degrees]C), indicating that a protein can fold on the 1- to 5-[micro]s time scale. Furthermore, the single-exponential nature of the relaxation indicates that the prefactor for transition state (TS)-folding models is probably [greater than or equal to] 1 [([micro]s).sup.-1] for a protein of this size and topology. Molecular dynamics simulations and IR spectroscopy provide a molecular rationale for the rapid, single-exponential folding of this protein. [[alpha].sub.3]D shows a significant bias toward local helical structure in the thermally denatured state. The molecular dynamics-simulated TS ensemble is highly heterogeneous and dynamic, allowing access to the TS via multiple pathways.

Author(s): Ugo Mayor [1]; Nicholas R. Guydosh [1]; Christopher M. Johnson [1]; J. Günter Grossmann [2]; Satoshi Sato [1]; Gouri S. Jas [3, 4]; Stefan M. V. Freund [1]; Darwin [...]

The authors review the publications on protein folding events. The topic of interest include the application of the experimental and theoretical methods of protein folding at atomic level resolution and their results.

Chemical synthesis allows the incorporation of nonnatural amino acids into proteins that may provide previously untried probes of their folding pathway and thermodynamic stability. We have used a flexible thioether linker as a loop mimetic in the human yes kinase-associated protein (YAP 65) WW domain, a three-stranded, 44-residue, [beta]-sheet protein. This linkage avoids problems of incorporating sequences that constrain loops to the extent that they significantly change the nature of the denatured state with concomitant effects on the folding kinetics. An NMR solution structure shows that the thioether linker had little effect on the global fold of the domain, although the loop is apparently more dynamic. The thioether variants are destabilized by up to 1.4 kcal/mol (1 cal = 4.18 J). Preliminary [PHI]-value analysis showed that the first loop is highly structured in the folding transition state, and the second loop is essentially unstructured. These data are consistent with results from simulated unfolding and detailed protein-engineering studies of structurally homologous WW domains. Previously, [PHI]-value analysis was limited to studying side-chain interactions. The linkers used here extend the protein engineering method directly to secondary-structure interactions.