Engineering Synthetic Electron Transfer Chains from Metallopeptide Membranes.

The energetic and geometric features enabling redox chemistry across the copper cupredoxin fold contain key components of electron transfer chains (ETC), which have been extended here by templating the cross-β bilayer assembly of a synthetic nonapeptide, HHQALVFFA-NH (K16A), with copper ions. Similar to ETC cupredoxin plastocyanin, these assemblies contain copper sites with blue-shifted ( 573 nm) electronic transitions and strongly oxidizing reduction potentials. Electron spin echo envelope modulation and X-ray absorption spectroscopies define square planar Cu(II) sites containing a single His ligand.

Advances in the World of Bacterial Microcompartments.

Bacterial microcompartments (MCPs) are extremely large (100-400 nm) and diverse proteinaceous organelles that compartmentalize multistep metabolic pathways, increasing their efficiency and sequestering toxic and/or volatile intermediates. This review highlights recent studies that have expanded our understanding of the diversity, structure, function, and potential biotechnological uses of MCPs. Several new types of MCPs have been identified and characterized revealing new functions and potential new associations with human disease.

Prokaryotic Organelles: Bacterial Microcompartments in and .

Bacterial microcompartments (MCPs) are proteinaceous organelles consisting of a metabolic pathway encapsulated within a selectively permeable protein shell. Hundreds of species of bacteria produce MCPs of at least nine different types, and MCP metabolism is associated with enteric pathogenesis, cancer, and heart disease. This review focuses chiefly on the four types of catabolic MCPs (metabolosomes) found in and : the propanediol utilization (), ethanolamine utilization (), choline utilization (), and glycyl radical propanediol () MCPs.

Genetic Characterization of a Glycyl Radical Microcompartment Used for 1,2-Propanediol Fermentation by Uropathogenic Escherichia coli CFT073.

Bacterial microcompartments (MCPs) are widespread protein-based organelles composed of metabolic enzymes encapsulated within a protein shell. The function of MCPs is to optimize metabolic pathways by confining toxic and/or volatile pathway intermediates. A major class of MCPs known as glycyl radical MCPs has only been partially characterized.

Molecular insights into the surface-catalyzed secondary nucleation of amyloid-β (Aβ) by the peptide fragment Aβ.

Understanding the structural mechanism by which proteins and peptides aggregate is crucial, given the role of fibrillar aggregates in debilitating amyloid diseases and bioinspired materials. Yet, this is a major challenge as the assembly involves multiple heterogeneous and transient intermediates. Here, we analyze the co-aggregation of Aβ and Aβ, two widely studied peptide fragments of Aβ implicated in Alzheimer's disease.

Dual Role of Ribosome-Binding Domain of NAC as a Potent Suppressor of Protein Aggregation and Aging-Related Proteinopathies.

The nascent polypeptide-associated complex (NAC) is a conserved ribosome-associated protein biogenesis factor. Whether NAC exerts chaperone activity and whether this function is restricted to de novo protein synthesis is unknown. Here, we demonstrate that NAC directly exerts chaperone activity toward structurally diverse model substrates including polyglutamine (PolyQ) proteins, firefly luciferase, and Aβ40.

Orientation of a Diagnostic Ligand Bound to Macroscopically Aligned Amyloid-β Fibrils Determined by Solid-State NMR.

With amyloid diseases poised to become a major health burden in countries with aging populations, diagnostic molecules that aid the detection of amyloid in vitro and in vivo are of considerable clinical value. Understanding how such ligands recognize their amyloid targets would help to design diagnostics that target specific amyloid types associated with a particular disease, but methods to provide comprehensive information are underdeveloped. Here, solid-state NMR is used to determine the molecular orientation of the amyloid diagnostic 1-fluoro-2,5-bis[( E)-3-carboxy-4-hydroxystyryl]-benzene (FSB) when bound to fibrils of the Alzheimer's amyloid-β polypeptide aligned on a planar substrate.

Increased sequence hydrophobicity reduces conformational specificity: A mutational case study of the Arc repressor protein.

The amino-acid sequences of soluble, globular proteins must have hydrophobic residues to form a stable core, but excess sequence hydrophobicity can lead to loss of native state conformational specificity and aggregation. Previous studies of polar-to-hydrophobic mutations in the β-sheet of the Arc repressor dimer showed that a single substitution at position 11 (N11L) leads to population of an alternate dimeric fold in which the β-sheet is replaced by helix. Two additional hydrophobic mutations at positions 9 and 13 (Q9V and R13V) lead to population of a differently folded octamer along with both dimeric folds.

Epigallocatechin-3-gallate remodels apolipoprotein A-I amyloid fibrils into soluble oligomers in the presence of heparin.

Amyloid deposits of WT apolipoprotein A-I (apoA-I), the main protein component of high-density lipoprotein, accumulate in atherosclerotic plaques where they may contribute to coronary artery disease by increasing plaque burden and instability. Using CD analysis, solid-state NMR spectroscopy, and transmission EM, we report here a surprising cooperative effect of heparin and the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG), a known inhibitor and modulator of amyloid formation, on apoA-I fibrils. We found that heparin, a proxy for glycosaminoglycan (GAG) polysaccharides that co-localize ubiquitously with amyloid , accelerates the rate of apoA-I formation from monomeric protein and associates with insoluble fibrils.

Molecular Origins of the Compatibility between Glycosaminoglycans and Aβ40 Amyloid Fibrils.

The Aβ peptide forms extracellular plaques associated with Alzheimer's disease. In addition to protein fibrils, amyloid plaques also contain non-proteinaceous components, including glycosaminoglycans (GAGs). We have shown previously that the GAG low-molecular-weight heparin (LMWH) binds to Aβ40 fibrils with a three-fold-symmetric (3Q) morphology with higher affinity than Aβ40 fibrils in alternative structures, Aβ42 fibrils, or amyloid fibrils formed from other sequences.

Amyloid plaques beyond Aβ: a survey of the diverse modulators of amyloid aggregation.

Aggregation of the amyloid-β (Aβ) peptide is strongly correlated with Alzheimer's disease (AD). Recent research has improved our understanding of the kinetics of amyloid fibril assembly and revealed new details regarding different stages in plaque formation. Presently, interest is turning toward studying this process in a holistic context, focusing on cellular components which interact with the Aβ peptide at various junctures during aggregation, from monomer to cross-β amyloid fibrils.

Atomic Details of the Interactions of Glycosaminoglycans with Amyloid-β Fibrils.

The amyloid plaques associated with Alzheimer's disease (AD) comprise fibrillar amyloid-β (Aβ) peptides as well as non-protein factors including glycosaminoglycan (GAG) polysaccharides. GAGs affect the kinetics and pathway of Aβ self-assembly and can impede fibril clearance; thus, they may be accessory molecules in AD. Here we report the first high-resolution details of GAG-Aβ fibril interactions from the perspective of the saccharide.

A role for indels in the evolution of Cro protein folds.

Insertions and deletions in protein sequences, or indels, can disrupt structure and may result in changes in protein folds during evolution or in association with alternative splicing. Pfl 6 and Xfaso 1 are two proteins in the Cro family that share a common ancestor but have different folds. Sequence alignments of the two proteins show two gaps, one at the N terminus, where the sequence of Xfaso 1 is two residues shorter, and one near the center of the sequence, where the sequence of Pfl 6 is five residues shorter.

A polymetamorphic protein.

Arc repressor is a homodimeric protein with a ribbon-helix-helix fold. A single polar-to-hydrophobic substitution (N11L) at a solvent-exposed position leads to population of an alternate dimeric fold in which 3₁₀ helices replace a β-sheet. Here we find that the variant Q9V/N11L/R13V (S-VLV), with two additional polar-to-hydrophobic surface mutations in the same β-sheet, forms a highly stable, reversibly folded octamer with approximately half the α-helical content of wild-type Arc.

The porous borders of the protein world.

Fold switching may play a role in the evolution of new protein folds and functions. He et al., in this issue of Structure, use protein design to illustrate that the same drastic change in a protein fold can occur via multiple different mutational pathways.