No abstract

Alzheimer’s disease (AD) is the most common neurodegenerative disease, and there are no mechanism-based therapies. AD is defined by the presence of abundant neurofibrillary lesions and neuritic plaques in cerebral cortex. Neurofibrillary lesions are made of paired helical and straight Tau filaments (PHFs and SFs), whereas Tau filaments with different morphologies characterize other neurodegenerative diseases. No high-resolution structures of Tau filaments are available. Here we present cryo-electron microscopy (cryo-EM) maps at 3.4–3.5 Å resolution and corresponding atomic models of PHFs and SFs from AD brain. Filament cores are made of two identical protofilaments comprising residues 306–378 of Tau, which adopt a combined cross-β/β-helix structure and define the seed for Tau aggregation. PHFs and SFs differ in their inter-protofilament packing, showing that they are ultrastructural polymorphs. These findings demonstrate that cryo-EM allows atomic characterization of amyloid filaments from patient-derived material, and pave the way to study a range of neurodegenerative diseases.

To facilitate understanding of, and access to, the information available for protein structures, we have constructed the Structural Classification of Proteins (scop) database. This database provides a detailed and comprehensive description of the structural and evolutionary relationships of the proteins of known structure. It also provides for each entry links to co-ordinates, images of the structure, interactive viewers, sequence data and literature references. Two search facilities are available. The homology search permits users to enter a sequence and obtain a list of any structures to which it has significant levels of sequence similarity. The key word search finds, for a word entered by the user, matches from both the text of the scop database and the headers of Brookhaven Protein Databank structure files. The database is freely accessible on World Wide Web (WWW) with an entry point to URL http: parallel scop.mrc-lmb.cam.ac.uk magnitude of scop.

The Structural Classification of Proteins (SCOP) database is a comprehensive ordering of all proteins of known structure, according to their evolutionary and structural relationships. The SCOP hierarchy comprises the following levels: Species, Protein, Family, Superfamily, Fold and Class. While keeping the original classification scheme intact, we have changed the production of SCOP in order to cope with a rapid growth of new structural data and to facilitate the discovery of new protein relationships. We describe ongoing developments and new features implemented in SCOP. A new update protocol supports batch classification of new protein structures by their detected relationships at Family and Superfamily levels in contrast to our previous sequential handling of new structural data by release date. We introduce pre-SCOP, a preview of the SCOP developmental version that enables earlier access to the information on new relationships. We also discuss the impact of worldwide Structural Genomics initiatives, which are producing new protein structures at an increasing rate, on the rates of discovery and growth of protein families and superfamilies. SCOP can be accessed at http://scop.mrc-lmb.cam.ac.uk/scop.

A novel folding motif has been observed in four different proteins which bind oligonucleotides or oligosaccharides: staphylococcal nuclease, anticodon binding domain of asp‐tRNA synthetase and B‐subunits of heat‐labile enterotoxin and verotoxin‐1. The common fold of the four proteins, which we call the OB‐fold, has a five‐stranded beta‐sheet coiled to form a closed beta‐barrel. This barrel is capped by an alpha‐helix located between the third and fourth strands. The barrel‐helix frameworks can be superimposed with r.m.s. deviations of 1.4–2.2 A, but no similarities can be observed in the corresponding alignment of the four sequences. The nucleotide or sugar binding sites, known for three of the four proteins, are located in nearly the same position in each protein: on the side surface of the beta‐barrel, where three loops come together. Here we describe the determinants of the OB‐fold, based on an analysis of all four structures. These proposed determinants explain how very different sequences adopt the OB‐fold. They also suggest a reinterpretation of the controversial structure of gene 5 ssDNA binding protein, which exhibits some topological and functional similarities with the OB‐fold proteins.

No abstract

The ordered assembly of tau protein into abnormal filamentous inclusions underlies many human neurodegenerative diseases. Tau assemblies seem to spread through specific neural networks in each disease, with short filaments having the greatest seeding activity. The abundance of tau inclusions strongly correlates with disease symptoms. Six tau isoforms are expressed in the normal adult human brain-three isoforms with four microtubule-binding repeats each (4R tau) and three isoforms that lack the second repeat (3R tau). In various diseases, tau filaments can be composed of either 3R or 4R tau, or of both. Tau filaments have distinct cellular and neuroanatomical distributions, with morphological and biochemical differences suggesting that they may be able to adopt disease-specific molecular conformations. Such conformers may give rise to different neuropathological phenotypes, reminiscent of prion strains. However, the underlying structures are not known. Using electron cryo-microscopy, we recently reported the structures of tau filaments from patients with Alzheimer's disease, which contain both 3R and 4R tau. Here we determine the structures of tau filaments from patients with Pick's disease, a neurodegenerative disorder characterized by frontotemporal dementia. The filaments consist of residues Lys254-Phe378 of 3R tau, which are folded differently from the tau filaments in Alzheimer's disease, establishing the existence of conformers of assembled tau. The observed tau fold in the filaments of patients with Pick's disease explains the selective incorporation of 3R tau in Pick bodies, and the differences in phosphorylation relative to the tau filaments of Alzheimer's disease. Our findings show how tau can adopt distinct folds in the human brain in different diseases, an essential step for understanding the formation and propagation of molecular conformers.

Specific modifications to histones are essential epigenetic markers---heritable changes in gene expression that do not affect the DNA sequence. Methylation of lysine 9 in histone H3 is recognized by heterochromatin protein 1 (HP1), which directs the binding of other proteins to control chromatin structure and gene expression. Here we show that HP1 uses an induced-fit mechanism for recognition of this modification, as revealed by the structure of its chromodomain bound to a histone H3 peptide dimethylated at Nzeta of lysine 9. The binding pocket for the N-methyl groups is provided by three aromatic side chains, Tyr21, Trp42 and Phe45, which reside in two regions that become ordered on binding of the peptide. The side chain of Lys9 is almost fully extended and surrounded by residues that are conserved in many other chromodomains. The QTAR peptide sequence preceding Lys9 makes most of the additional interactions with the chromodomain, with HP1 residues Val23, Leu40, Trp42, Leu58 and Cys60 appearing to be a major determinant of specificity by binding the key buried Ala7. These findings predict which other chromodomains will bind methylated proteins and suggest a motif that they recognize.