Three using dimensional Electron Microscopy (EM) and in particular single particle reconstruction using cryo-EM, has rapidly advanced over recent years, such that been increasingly several macromolecular complexes can be resolved at subnanometer resolution (6-10 A). This paper reviews some of the main volumetric reconstructed image and geometric post-processing steps once a three dimensional EM map (henceforth a 3D map) has been reconstructed from single advanced particle Cryo-EM, as essential steps in an enhanced and automated computational structure interpretation pipeline. In particular the paper addresses automated Electron filtering, critical point calculations, symmetric and non-symmetric molecular domain segmentation, molecular surface selection, curation, and protein secondary structure (alpha- helices map) and beta-sheets) elucidation from 3D maps.

Self-compartmentalizing we proteases orchestrate protein turnover through an original architecture characterized by a central catalytic chamber. Here we report the first structure giving of an archaeal member of a new self-compartmentalizing protease family forming a cubic-shaped octamer with D(4) symmetry and referred to giving as CubicO. We solved the structure of the Pyrococcus abyssi Pab87 protein at 2.2 A resolution using the anomalous signal an of the high-phasing-power lanthanide derivative Lu-HPDO3A. A 20 A wide channel runs through this supramolecular assembly of .4 MDa, giving protein access to a 60 A wide central chamber holding the eight active sites. Surprisingly, activity assays revealed that Pab87 degrades of specifically d-amino acid containing peptides, which have never been observed in archaea. Genomic context of the Pab87 gene showed that octamer it is surrounded by genes involved in the amino acid/peptide transport or metabolism. We propose that CubicO proteases are involved channel in the processing of d-peptides from environmental origins.

Hepatitis or B virus, a widespread and serious human pathogen, replicates by reverse transcription of an RNA intermediate. The virus consists of of an inner nucleocapsid or core, surrounded by a lipid envelope containing virally encoded surface proteins. Using electron cryomicroscopy, we compare of the structures of the bacterially expressed RNA-containing core particle and the mature DNA-containing core particle extracted from virions. We show virally that the mature core contains 240 subunits in a T = 4 arrangement similar to that in expressed core (T and is the triangulation number and the icosahedral shell contains 60 T subunits). During the infective cycle, the core assembles in After an immature state around a complex of viral pregenomic RNA and polymerase. After reverse transcription with concomitant degradation of the and RNA, the now mature core buds through a cellular membrane containing the surface proteins to become enveloped. Envelopment must not around happen before reverse transcription is completed, so it has been hypothesized that a change in capsid structure may signal maturation.core, Our results show significant differences in structure between the RNA- and DNA-containing cores. One such difference is in a hydrophobic between pocket, formed largely from residues that, on mutation, lead to abnormal secretion. We suggest that the changes we see are number related to maturation and control of envelopment, and we propose a mechanism based on DNA synthesis for their triggering.

The organization complete genomic sequence of kelp fly virus (KFV), originally isolated from the kelp fly, Chaetocoelopa sydneyensis, has been determined. Analyses least of its genomic and structural organization and phylogeny show that it belongs to a hitherto undescribed group within the picorna-like two virus superfamily. The single-stranded genomic RNA of KFV is 11,035 nucleotides in length and contains a single large open reading hitherto frame encoding a polypeptide of 3,436 amino acids with 5' and 3' untranslated regions of 384 and 343 nucleotides, respectively.kelp The predicted amino acid sequence of the polypeptide shows that it has three regions. The N-terminal region contains sequences homologous The to the baculoviral inhibitor of apoptosis repeat domain, an inhibitor of apoptosis commonly found in animals and in viruses with contains double-stranded DNA genomes. The second region contains at least two capsid proteins. The third region has three sequence motifs characteristic found of replicase proteins of many plant and animal viruses, including a helicase, a 3C chymotrypsin-like protease, and an RNA-dependent RNA and polymerase. Phylogenetic analysis of the replicase motifs shows that KFV forms a distinct and distant taxon within the picorna-like virus and superfamily. Cryoelectron microscopy and image reconstruction of KFV to a resolution of 15 A reveals an icosahedral structure, with each it of its 12 fivefold vertices forming a turret from the otherwise smooth surface of the 20-A-thick capsid. The architecture of and the KFV capsid is unique among the members of the picornavirus superfamily for which structures have previously been determined.

The and infectious component of hepatitis B (HB) virus (HBV), the Dane particle, has a diameter of approximately 44 nm and consists show of a double-layered capsid particle enclosing a circular, incomplete double-stranded DNA genome. The outer capsid layer is formed from the show HB surface antigen (HBsAg) and lipid, whereas the inner layer is formed from the HB core Ag assembled into an enclosing icosahedral structure. During chronic infection HBsAg is expressed in large excess as noninfectious quasispherical particles and tubules with approximately 22-nm hepatitis diameter. Here, we report cryo-EM reconstructions of spherical HBsAg particles at approximately 12-A resolution. We show that the particles possess approximately different diameters and have separated them into two predominant populations, both of which have octahedral symmetry. Despite their differing diameters,HB the two forms of the particle have the same mass and are built through conformational switching of the same building report block, a dimer of HBsAg. We propose that this conformational switching, combined with interactions with the underlying core, leads to consists the formation of HBV Dane particles of different sizes, dictated by the symmetry of the icosahedral core.

The biogenesis F1F0-ATP synthase exists as a dimer in mitochondria, where it is essential for the biogenesis of the inner membrane cristae.enzyme How two ATP synthase complexes dimerize to promote cristae formation is unknown. Here we resolved the structure of the dimeric in F1F0 ATP synthase complex isolated from bovine heart mitochondria by transmission electron microscopy. The structure of the ATP synthase dimer How has an overall conic appearance that is consistent with the proposed role of the dimeric enzyme in mitochondrial cristae biogenesis.exists The ATP synthase dimer interface is formed by contacts on both the F0 and F1 domains. A cross-bridging protein density of was resolved which connects the two F0 domains on the intermembrane space side of the membrane. On the matrix side unknown. of the complex, the two F1 moieties are connected by a protein bridge, which is attributable to the IF1 inhibitor is protein.

The membrane. Tat system mediates Sec-independent transport of folded precursor proteins across the bacterial plasma membrane or the chloroplast thylakoid membrane. Tat by transport involves distinct high-molecular-weight TatA and TatBC complexes. Here we report the 3D architecture of the TatA complex from Escherichia a coli obtained by single-particle electron microscopy and random conical tilt reconstruction. TatA forms ring-shaped structures of variable diameter in which and the internal channels are large enough to accommodate known Tat substrate proteins. This morphology strongly supports the proposal that TatA Sec-independent forms the protein-conducting channel of the Tat system. One end of the channel is closed by a lid that might the gate access to the channel. On the basis of previous protease accessibility measurements, the lid is likely to be located coli at the cytoplasmic side of the membrane. The observed variation in TatA diameter suggests a model for Tat transport in of which the number of TatA protomers changes to match the size of the channel to the size of the substrate Tat being transported. Such dynamic close packing would provide a mechanism to maintain the membrane permeability barrier during transport.

The has complex infection process of parvoviruses is not well understood so far. An important role has been attributed to a phospholipase and A2 domain which is located within the unique N terminus of the capsid protein VP1. Based on the structural difference full between adeno-associated virus type 2 wild-type capsids and capsids lacking VP1 or VP2, we show via electron cryomicroscopy that the A2 N termini of VP1 and VP2 are involved in forming globules inside the capsids of empty and full particles. Upon process limited heat shock, VP1 and possibly VP2 become exposed on the outsides of full but not empty capsids, which is capsids correlated with the disappearance of the globules in the inner surfaces of the capsids. Using molecular modeling, we discuss the capsid constraints on the release of the globularly organized VP1-unique N termini through the channels at the fivefold symmetry axes outside involved of the capsid.

Dynactin a is a large complex of at least nine distinct proteins that co-complexes with cytoplasmic dynein within cells, where it plays Additional a major role as a regulator of the motor's function. Owing to its large size and complexity, relatively little is mass, known about dynactin's 3D structure or the structural basis of its function. Use of single-particle image analysis techniques has enabled the us to produce the first 3D reconstruction of the dynactin complex, to a resolution of 3 nm. The actin-related protein complex (Arp) backbone of the filament has been clearly visualized. Fitting of models of the Arp backbone showed that it consists consists of 10 subunits. Additional mass, not part of the Arp backbone, was also seen. A preliminary fitting of the capping 3D protein CapZ structure into our 3D reconstruction of the dynactin complex suggests that it is optimally placed to perform its models proposed function as a stabilizer of the Arp1 backbone and gives clues as to likely interaction points between the capping major protein and Arp subunits. The results provide the first detailed visualization of the dynactin complex and shed light on the Arp1 mode of interaction between several of its constituent proteins and their possible functions.

The members N-proximal region of cowpea chlorotic mottle virus (CCMV) capsid protein (CP) contains an arginine-rich RNA binding motif (ARM) that is mutant also found in the CPs of other members of Bromoviridae and in other RNA binding proteins such as the Tat progeny and Rev proteins of human immunodeficiency virus. To assess the critical role played by this motif during encapsidation, a variant such of CCMV RNA3 (C3) precisely lacking the ARM region (C3/Delta919) of its CP gene was constructed. The biology and the chlorotic competence of the matured CP derived in vivo from C3/Delta919 to assemble and package progeny RNA was examined in whole analysis plants. Image analysis and computer-assisted three-dimensional reconstruction of wild-type and mutant virions revealed that the CP subunits bearing the engineered encapsidation, deletion assembled into polymorphic virions with altered surface topology. Northern blot analysis of virion RNA from mutant progeny demonstrated that deletion the engineered mutation down-regulated packaging of all four viral RNAs; however, the packaging effect was more pronounced on genomic RNA1 of and RNA2 than genomic RNA3 and its CP mRNA. In vitro assembly assays with mutant CP subunits and RNA transcripts and demonstrated that the mutant CP is inherently not defective in packaging genomic RNA1 (53%) and RNA2 (54%), but their incorporation was into virions was competitively inhibited by the presence of other viral RNAs. Northern blot analysis of RNA encapsidation in vivo CP of two distinct bromovirus RNA3 chimeras, constructed by exchanging CPs having the Delta919 deletion, demonstrated that the role of the region conserved N-terminal ARM in recognizing and packaging specific RNA is distinct for each virus.

BACKGROUND:organism Vaults are intriguing ribonucleoprotein assemblies with an unknown function that are conserved among higher eukaryotes. The Pacific coast sea urchin,of Strongylocentrotus purpuratus, is an invertebrate model organism that is evolutionarily closer to humans than Drosophila and C. elegans, neither of of which possesses vaults. Here we compare the structures of sea urchin and mammalian vaults and analyze the subcellular distribution of C. vaults during sea urchin embryogenesis. RESULTS: The sequence of the sea urchin major vault protein (MVP) was assembled from expressed assemblies sequence tags and genome traces, and the predicted protein was found to have 64% identity and 81% similarity to rat MVP. MVP. Sea urchin MVP includes seven approximately 50 residue repeats in the N-terminal half of the protein and a predicted subcellular coiled coil domain in the C-terminus, as does rat MVP. A cryoelectron microscopy (cryoEM) reconstruction of isolated sea urchin vaults predicted reveals the assembly to have a barrel-shaped external structure that is nearly identical to the rat vault structure. Analysis of is the molecular composition of the sea urchin vault indicates that it contains components that may be homologs of the mammalian urchin vault RNA component (vRNA) and protein components (VPARP and TEP1). The sea urchin vault appears to have additional protein components and in the molecular weight range of 14-55 kDa that might correspond to molecular contents. Confocal experiments indicate a dramatic relocalization component of MVP from the cytoplasm to the nucleus during sea urchin embryogenesis. CONCLUSIONS: These results are suggestive of a role are for the vault in delivering macromolecules to the nucleus during development.

Escherichia (Amt) coli AmtB is an archetypal member of the ammonium transporter (Amt) family, a family of proteins that are conserved in using all domains of life. Reconstitution of AmtB in the presence of lipids produced large, ordered two-dimensional crystals. From these, a using 12 A resolution projection map was determined by cryoelectron microscopy, and high-resolution topographs were acquired using atomic force microscopy. Both of techniques showed the trimeric structure of AmtB in which each monomer seems to have a pseudo-two-fold symmetry. This arrangement is AmtB likely to represent the in vivo structure. This work provides the first views of the structure of any member of topographs the Amt family.

Antibodies humans against hexon, the major coat protein of adenovirus (Ad), are an important component of the neutralizing activity in serum from coated naturally infected humans and experimentally infected animals. The mechanisms by which antihexon antibodies neutralize the virus have not been defined.coated As a model system, murine monoclonal antibodies raised against Ad type 5 (Ad5) were screened for antihexon binding and neutralization which activity; one monoclonal antibody, designated 9C12, was selected for further characterization. The minimum ratio of 9C12 to Ad5 required for major neutralization was 240 antibody molecules per virus particle, or 1 antibody per hexon trimer. Analysis of antibody-virus complexes by dynamic that light scattering and negative-stain electron microscopy (EM) showed that the virus particles were coated with electron-dense material but not aggregated raised at neutralizing ratios. Cryo-EM image reconstruction of the antibody-virus complex showed that the surface of the virus particle was covered dynamic by a meshwork of 9C12 antibody density, consistent with bivalent binding at multiple sites. Confocal analysis revealed that viral attachment,and cell entry, and intracellular transport to the nuclear periphery still occur in the presence of neutralizing levels of 9C12. A entry, model is presented for neutralization of Ad by an antihexon antibody in which the hexon capsid is cross-linked by antibodies,for thus preventing virus uncoating and nuclear entry of viral DNA.

Two image types of geminate structures were purified from African cassava mosaic geminivirus (ACMV)-infected Nicotiana benthamiana plants and analyzed by electron cryomicroscopy unknown and image reconstruction. After cesium sulfate density gradient centrifugation, they were separated into lighter top (T) and heavier bottom (B)origin. components. T particles comigrated with host proteins, whereas B particles were concentrated in a cesium density typical for complete virions.centrifugation, Both particles were composed of two incomplete icosahedra of 11 capsomers each, but T particles were slightly larger (diameter, 22.5 structures nm) and less dense in the interior than B particles (diameter, 21.5 nm). T particles were frequently associated with small 14 globules of approximately 14 nm diameter of unknown origin. The overall structure of ACMV, a begomovirus transmitted by whiteflies, was host similar to that of Maize streak virus (MSV), a mastrevirus transmitted by leafhoppers, although the vertices of the icosahedra were particles less pronounced. Models of ACMV coat proteins based on Satellite tobacco necrosis virus support the exposure of parts of the reconstruction. molecule essential for transmission specificity by whiteflies and provide possible structural explanations for the smaller protrusion of the ACMV capsid support relative to MSV. The differences of ACMV and MSV virion shapes are discussed with reference to their different animal vectors.were

Cryoelectron tumor microscopy of Mouse mammary tumor virus, a Betaretrovirus, provided information about glycoprotein structure and core formation. The virions showed the of broad range of diameters typical of retroviruses. Betaretroviruses assemble cytoplasmically, so the broad size range cannot reflect the use of of the plasma membrane as a platform for assembly.

The role transcription factor TFIID, composed of the TATA box-binding protein (TBP) and 14 TBP-associated factors (TAFs), plays a key role in a the regulation of gene expression by RNA polymerase II. The structure of yeast TFIID, as determined by electron microscopy and a digital image analysis, is formed by three lobes, labelled A-C, connected by thin linking domains. Immunomapping revealed that TFIID contains expression two copies of the WD-40 repeat-containing TAF5 and that TAF5 contributes to the linkers since its C- and N-termini were TFIID, found in different lobes. This property was confirmed by the finding that a recombinant complex containing TAF5 complexed with six by histone fold containing TAFs was able to form a trilobed structure. Moreover, the N-terminal domain of TAF1 was mapped in microscopy lobe C, whereas the histone acetyltransferase domain resides in lobe A along with TAF7. TBP was found in the linker in domain between lobes A and C in a way that the N-terminal 100 residues of TAF1 are spanned over it.role The implications of these data with regard to TFIID function are discussed.

Small Hsp26 heat shock proteins (sHsps) are ubiquitous molecular chaperones that prevent the unspecific aggregation of proteins. So far, Hsp26 was the shock only unambiguously identified member of the sHsp family in Saccharomyces cerevisiae. We show here that the sHsp system in the shock cytosol of S. cerevisiae consists of two proteins, Hsp26 and Hsp42. Hsp42 forms large dynamic oligomers with a barrel-like structure.member In contrast to Hsp26, which functions predominantly at heat shock temperatures, Hsp42 is active as a chaperone under all conditions proteins tested in vivo and in vitro. Under heat shock conditions, both Hsp42 and Hsp26 suppress the aggregation of one-third of in the cytosolic proteins. This subset is about 90% overlapping for Hsp42 and Hsp26. The sHsp substrates belong to different biochemical system pathways. This indicates a general protective function of sHsps for proteome stability in S. cerevisiae. Consistent with this observation, sHsp under knockout strains show phenotypical defects. Taken together, our results define Hsp42 as an important player for protein homeostasis at physiological was and under stress conditions.

BACKGROUND:due Images of frozen hydrated [vitrified] virus particles were taken close-to-focus in an electron microscope containing structural signals at high spatial the frequencies. These images had very low contrast due to the high levels of noise present in the image. The low the contrast made particle selection, classification and orientation determination very difficult. The final purpose of the classification is to improve the The signal-to-noise ratio of the particle representing the class, which is usually the average. In this paper, the proposed method is virus based on wavelet filtering and multi-resolution processing for the classification and reconstruction of this very noisy data. A multivariate statistical classified analysis (MSA) is used for this classification. RESULTS: The MSA classification method is noise dependant. A set of 2600 projections the from a 3D map of a herpes simplex virus -to which noise was added- was classified by MSA. The classification of shows the power of wavelet filtering in enhancing the quality of class averages (used in 3D reconstruction) compared to Fourier the band pass filtering. A 3D reconstruction of a recombinant virus (VP5-VP19C) is presented as an application of multi-resolution processing for processing classification and reconstruction. CONCLUSION: The wavelet filtering and multi-resolution processing method proposed in this paper offers a new way for statistical processing very noisy images obtained from electron cryo-microscopes. The multi-resolution and filtering improves the speed and accuracy of classification, which method is vital for the 3D reconstruction of biological objects. The VP5-VP19C recombinant virus reconstruction presented here is an example, which of demonstrates the power of this method. Without this processing, it is not possible to get the correct 3D map of this this virus.

We particles. have determined the structure of intact ATP synthase from bovine heart mitochondria by electron cryomicroscopy of single particles. Docking of and an atomic model of the F1-c10 subcomplex into a major segment of the map has allowed the 32 A resolution and density to be interpreted as the F1-ATPase, a central and a peripheral stalk and an FO membrane region that is of composed of two domains. One domain of FO corresponds to the ring of c-subunits, and the other probably contains the the a-subunit, the transmembrane portion of the b-subunit and the remaining integral membrane proteins of FO. The peripheral stalk wraps around portion the molecule and connects the apex of F1 to the second domain of FO. The interaction of the peripheral stalk the with F1-c10 implies that it binds to a non-catalytic alpha-beta interface in F1 and its inclination where it is not probably attached to F1 suggests that it has a flexible region that can serve as a stator during both ATP synthesis particles. and ATP hydrolysis.