We show that the cytotoxicity of water-soluble fullerene species is a sensitive function of surface derivatization; in two different human cell lines, the lethal dose of fullerene changed over 7 orders of magnitude with relatively minor alterations in fullerene structure. In particular, an aggregated form of C60, the least derivatized of the four materials, was substantially more toxic than highly soluble derivatives such as C3, Na+ 2 - 3[C60O7 - 9(OH)12 - 15](2-3)-, and C60(OH)24. Oxidative damage to the cell membranes was observed in all cases where fullerene exposure led to cell death. We show that under ambient conditions in water fullerenes can generate superoxide anions and postulate that these oxygen radicals are responsible for membrane damage and subsequent cell death. This work demonstrates both a strategy for enhancing the toxicity of fullerenes for certain applications such as cancer therapeutics or bactericides, as well as a remediation for the possible unwarranted biological effects of pristine fullerenes.

Motors generating mechanical force, powered by the hydrolysis of ATP, translocate doublestranded DNA into preformed capsids (proheads) of bacterial viruses 1,2 and certain animal viruses 3 . Here we describe the motor that packages the double-stranded DNA of the Bacillus subtilis bacteriophage ϕ29 into a precursor capsid. We determined the structure of the head-tail connector-the central component of the ϕ29 DNA packaging motor-to 3.2Å resolution by means of X-ray crystallography. We then fitted the connector into the electron densities of the prohead and of the partially packaged prohead as determined using cryo-electron microscopy and image reconstruction analysis. Our results suggest that the prohead plus dodecameric connector, prohead RNA, viral ATPase and DNA comprise a rotary motor with the head-prohead RNAATPase complex acting as a stator, the DNA acting as a spindle, and the connector as a ball-race. The helical nature of the DNA converts the rotary action of the connector into translation of the DNA.The bacteriophage ϕ29 (Fig. 1) is a 19-kilobase (19-kb) double-stranded DNA (dsDNA) virus with a prolate head and complex structure 4 . The prohead (Fig. 1), into which the DNA is packaged, is about 540Å long and 450Å wide 5 . The ϕ29 connector, a cone-shaped dodecamer of gene product 10 (gp10), occupies the pentagonal vertex at the base of the prohead 5 and is the portal for DNA entry during packaging and DNA ejection during infection 6 . The connector, in association with the oligomeric, ϕ29-encoded prohead RNA (pRNA) and a viral ATPase (gp16), is required for DNA packaging [7][8][9] . However, only the first 120 bases of the 174-base pRNA are essential for packaging 7 the genomic dsDNA with gp3 (DNA-gp3) can be packaged into proheads in about three minutes in vitro (P.J.J., unpublished results). The connector proteins of tailed phages 6 vary in relative molecular mass (M r ) from 36,000 (36K) in ϕ29 to 83K in phage P22, and assemble into oligomers with a central channel. The structure of the isolated ϕ29 connector has been studied by atomic force microscopy 10 and cryo-electron microscopy (cryo-EM) of two-dimensional arrays 11 , immuno-electron microscopy 12 and X-ray crystallography 13,14 .The connector structure, as now determined by X-ray crystallography, can be divided into three, approximately cylindrical regions: the narrow end, the central part, and the wide end, having external radii (Å ) of 33, 47 and 69, respectively (Fig. 2). These regions are respectively 25, 28 and 22Å in height, making the total connector 75Å long. The internal channel has a diameter of about 36Å at the narrow end, increasing to 60Å at the wide end.Comparison with electron microscopy reconstructions 5,11 shows that the narrow end protrudes from the portal vertex of the phage head, is associated with the multimeric pRNA, and binds the lower collar in the mature virus.The electron density of the connector was interpreted in terms of the amino-acid sequence 15 and was confirmed by the two Hg sites (see Methods section)...

Upon contact with water, under a variety of conditions, C60 spontaneously forms a stable aggregate with nanoscale dimensions (d = 25−500 nm), termed here “nano-C60”. The color, hydrophobicity, and reactivity of individual C60 are substantially altered in this aggregate form. Herein, we provide conclusive lines of evidence demonstrating that in solution these aggregates are crystalline in order and remain as underivatized C60 throughout the formation/stabilization process that can later be chemically reversed. Particle size can be affected by formation parameters such as rates and the pH of the water addition. Once formed, nano-C60 remains stable in solution at or below ionic strengths of 0.05 I for months. In addition to demonstrating aggregate formation and stability over a wide range of conditions, results suggest that prokaryotic exposure to nano-C60 at relatively low concentrations is inhibitory, indicated by lack of growth (≥0.4 ppm) and decreased aerobic respiration rates (4 ppm). This work demonstrates the fact that the environmental fate, distribution, and biological risk associated with this important class of engineered nanomaterials will require a model that addresses not only the properties of bulk C60 but also that of the aggregate form generated in aqueous media.

Influenza A viruses pose a serious threat to world public health, particularly the currently circulating avian H5N1 viruses. The influenza viral nucleoprotein forms the protein scaffold of the helical genomic ribonucleoprotein complexes, and has a critical role in viral RNA replication. Here we report a 3.2 A crystal structure of this nucleoprotein, the overall shape of which resembles a crescent with a head and a body domain, with a protein fold different compared with that of the rhabdovirus nucleoprotein. Oligomerization of the influenza virus nucleoprotein is mediated by a flexible tail loop that is inserted inside a neighbouring molecule. This flexibility in the tail loop enables the nucleoprotein to form loose polymers as well as rigid helices, both of which are important for nucleoprotein functions. Single residue mutations in the tail loop result in the complete loss of nucleoprotein oligomerization. An RNA-binding groove, which is found between the head and body domains at the exterior of the nucleoprotein oligomer, is lined with highly conserved basic residues widely distributed in the primary sequence. The nucleoprotein structure shows that only one of two proposed nuclear localization signals are accessible, and suggests that the body domain of nucleoprotein contains the binding site for the viral polymerase. Our results identify the tail loop binding pocket as a potential target for antiviral development.

The reovirus polymerase and those of other dsRNA viruses function within the confines of a protein capsid to transcribe the tightly packed dsRNA genome segments. The crystal structure of the reovirus polymerase, lambda3, determined at 2.5 A resolution, shows a fingers-palm-thumb core, similar to those of other viral polymerases, surrounded by major N- and C-terminal elaborations, which create a cage-like structure, with four channels leading to the catalytic site. This "caged" polymerase has allowed us to visualize the results of several rounds of RNA polymerization directly in the crystals. A 5' cap binding site on the surface of lambda3 suggests a template retention mechanism by which attachment of the 5' end of the plus-sense strand facilitates insertion of the 3' end of the minus-sense strand into the template channel.

Rotavirus RNA-dependent RNA polymerase, VP1, catalyzes RNA synthesis within a subviral particle. This activity depends on core shell protein VP2. A conserved sequence at the 3′ end of plus-strand RNA templates is important for polymerase association and genome replication. We have determined the structure of VP1 at 2.9 Å resolution, as apoenzyme and in complex with RNA. The cage-like enzyme is similar to reovirus λ3, with four tunnels leading to or from a central, catalytic cavity. A distinguishing characteristic of VP1 is specific recognition, by conserved features of the template-entry channel, of four bases, UGUG, in the conserved 3′ sequence. Well-defined interactions with these bases position the RNA so that its 3′ end overshoots the initiating register, producing a stable but catalytically inactive complex. We propose that specific 3′ end recognition selects rotavirus RNA for packaging and that VP2 activates the auto-inhibited VP1/RNA complex to coordinate packaging and genome replication.

Histone modifications, such as the frequently occurring lysine succinylation1,2, are central to the regulation of chromatin-based processes. However, the mechanism and functional consequences of histone succinylation are unknown. Here we show that the α-ketoglutarate dehydrogenase (α-KGDH) complex is localized in the nucleus in human cell lines and binds to lysine acetyltransferase 2A (KAT2A, also known as GCN5) in the promoter regions of genes. We show that succinyl-coenzyme A (succinyl-CoA) binds to KAT2A. The crystal structure of the catalytic domain of KAT2A in complex with succinyl-CoA at 2.3 Å resolution shows that succinyl-CoA binds to a deep cleft of KAT2A with the succinyl moiety pointing towards the end of a flexible loop 3, which adopts different structural conformations in succinyl-CoA-bound and acetyl-CoA-bound forms. Site-directed mutagenesis indicates that tyrosine 645 in this loop has an important role in the selective binding of succinyl- CoA over acetyl-CoA. KAT2A acts as a succinyltransferase and succinylates histone H3 on lysine 79, with a maximum frequency around the transcription start sites of genes. Preventing the α-KGDH complex from entering the nucleus, or expression of KAT2A(Tyr645Ala), reduces gene expression and inhibits tumour cell proliferation and tumour growth. These findings reveal an important mechanism of histone modification and demonstrate that local generation of succinyl-CoA by the nuclear α-KGDH complex coupled with the succinyltransferase activity of KAT2A is instrumental in histone succinylation, tumour cell proliferation, and tumour development.

Hepatitis E virus (HEV), a small, non-enveloped RNA virus in the familyHepeviridae, is associated with endemic and epidemic acute viral hepatitis in developing countries. Our 3.5-Å structure of a HEV-like particle (VLP) shows that each capsid protein contains 3 linear domains that form distinct structural elements: S, the continuous capsid; P1, 3-fold protrusions; and P2, 2-fold spikes. The S domain adopts a jelly-roll fold commonly observed in small RNA viruses. The P1 and P2 domains both adopt ␤-barrel folds. Each domain possesses a potential polysaccharide-binding site that may function in cell-receptor binding. Sugar binding to P1 at the capsid protein interface may lead to capsid disassembly and cell entry. Structural modeling indicates that native T ‫؍‬ 3 capsid contains flat dimers, with less curvature than those of T ‫؍‬ 1 VLP. Our findings significantly advance the understanding of HEV molecular biology and have application to the development of vaccines and antiviral medications.capsid ͉ HEV V iral hepatitis is principally caused by 5 distinct viruses named hepatitis A-E. Despite their similar names, the 5 viruses are unrelated, and they have totally different genome structures with distinct replication mechanisms. Hepatitis E virus (HEV) is responsible for endemic hepatitis as well as sporadic epidemics of acute, enterically transmitted hepatitis in the developing world, including parts of Asia, the Middle East, Africa, and Mexico (1, 2). HEV accounts for more than 50% of acute viral hepatitides in young adults in these regions, with a case fatality of 1-2% in regular patients and up to 20% in pregnant women.Given the lack of a robust cell culture system, and because HEV is not closely related to any other well-characterized virus, little is known about the molecular biology of HEV or its strategy for replication (1). HEV is a small, non-enveloped virus with a 7.2 kb, positive-sense RNA genome. Its genomic RNA is polyadenylated and contains 3 ORFs. Located near the 5Ј-end, ORF1 encodes a non-structural polyprotein with multiple functional domains, including those for methyltransferase, protease, helicase, and polymerase. The viral capsid protein (CP) is encoded by ORF2 near the 3Ј-end. ORF3, which partially overlaps with the other 2 ORFs, codes for an immunogenic protein of unknown function. HEV was originally classified in the Caliciviridae family because of its structural similarity to other caliciviruses; however, it is now the sole member of the Hepeviridae family. The genomic RNA of HEV exhibits several distinct features compared to the genomic RNA of caliciviruses, including a methylated cap at the 5Ј-end and an ORF1 with functional domains arranged in a different order (1, 3).Previous studies of HEV assembly have primarily focused on the overexpression of viral proteins. The ORF2 capsid protein, HEV-CP, contains a total of 660 amino acid residues. At the HEV-CP N terminus is a signal peptide followed by an arginine-rich domain that potentially play a role in viral RNA encapsidation during assem...