T-cell antigen receptors composed of gamma and delta polypeptide chains (gammadelta TCRs) can directly recognize antigens in the form of intact proteins or non-peptide compounds, unlike alphabeta TCRs, which recognize antigens bound to major histocompatibility complex molecules (MHC). About 5% of peripheral blood T cells bear gammadelta TCRs, most of which recognize non-peptide phosphorylated antigens. Here we describe the 3.1 A resolution structure of a human gammadelta TCR from a T-cell clone that is phosphoantigen-reactive. The orientation of the variable (V) and constant (C) regions of the gammadelta TCR is unique when compared with alphabeta TCRs or antibodies, and results from an unusually small angle between the Vgamma and Cgamma domains. The complementarity-determining regions (CDRs) of the V domains exhibit a chemically reasonable binding site for phosphorylated antigens, providing a possible explanation for the canonical usage of the Vgamma9 and Vdelta2 gene segments by phosphoantigen-reactive receptors. Although the gammadelta TCR V domains are similar in overall structure to those of alphabeta TCRs, gammadelta TCR C domains are markedly different. Structural differences in Cgamma and Cdelta, and in the location of the disulphide bond between them, may enable gammadelta TCRs to form different recognition/signalling complexes than alphabeta TCRs.

HIV/AIDS continues to be a menace to public health. Several drugs currently on the market have successfully improved the ability to manage the viral burden in infected patients. However, new drugs are needed to combat the rapid emergence of mutated forms of the virus that are resistant to existing therapies. Currently, approved drugs target three of the four major enzyme activities encoded by the virus that are critical to the HIV life cycle. Although a number of inhibitors of HIV RNase H activity have been reported, few inhibit by directly engaging the RNase H active site. Here, we describe structures of naphthyridinone-containing inhibitors bound to the RNase H active site. This class of compounds binds to the active site via two metal ions that are coordinated by catalytic site residues, D443, E478, D498, and D549. The directionality of the naphthyridinone pharmacophore is restricted by the ordering of D549 and H539 in the RNase H domain. In addition, one of the naphthyridinone-based compounds was found to bind at a second site close to the polymerase active site and non-nucleoside/nucleotide inhibitor sites in a metal-independent manner. Further characterization, using fluorescence-based thermal denaturation and a crystal structure of the isolated RNase H domain reveals that this compound can also bind the RNase H site and retains the metal-dependent binding mode of this class of molecules. These structures provide a means for structurally guided design of novel RNase H inhibitors.

Although eradicated from nature more than two decades ago, the threat of smallpox has reemerged because of concerns over its use as a biological weapon. We present the structure of the poxvirus L1 protein, a molecule that is conserved throughout the poxvirus family and is nearly identical in vaccinia virus and in variola virus, which causes smallpox. L1 is a myristoylated envelope protein that is a potent target for neutralizing antibodies and an important component of current experimental vaccines. The L1 structure reveals a hydrophobic cavity located adjacent to its N terminus. The cavity would be capable of shielding the myristate moiety, which is essential for virion assembly. The structure of L1 is a step in the elucidation of molecular mechanisms common to all poxviruses that may stimulate the design of safer vaccines and new antipoxvirus drugs.myristoylation ͉ virion protein ͉ x-ray structure P oxviruses are a family of large DNA viruses, the most infamous of which is variola virus, the cause of smallpox. After the worldwide eradication of smallpox more than two decades ago by immunization with the closely related vaccinia virus, routine immunization against smallpox ceased (1). With the threat of an intentional release of variola virus and the emergence of monkeypox virus that also infects humans, the development of antiviral drugs and safer vaccines has been urged (2). By better understanding mechanisms involved in poxvirus biology, therapeutics and vaccines can be designed to act against the whole family of poxviruses (3).Poxviruses have Ϸ200 genes and a complex life cycle. After entry into the host cell, the virus reproduces in the cytoplasm, encoding its own replication machinery and transcription factors. Maturing vaccinia virions undergo a transformation from spherical immature particles to the brick-shaped intracellular mature virions (IMVs) that have lipid membranes and are the first infectious form of the virus. Most IMVs are released directly by lysis of the host cell. Some IMVs acquire additional membranes and are then transported out through the host cell membrane. They can either remain attached to the outside of the cell or detach from the cell as an extracellular enveloped virus (EEV). Disruption of the EEV exterior membrane, either by mechanical force or by host complement factors, can also release the IMV form (4). Vaccine development is targeting proteins from each form (5, 6), although because of the fragile nature of the EEV outermost membrane, the IMV form of the virus is thought to play the major role in host-to-host transmission (7).L1 (also called L1R) is a myristoylated transmembrane protein of 250 residues that is expressed on the surface of the IMV form of the virus. It is an essential protein because vaccinia viruses with the L1 gene deleted are not capable of maturation (8). Although L1 has a C-terminal hydrophobic segment embedded in the viral membrane, the 185-residue, disulfide-bonded ectodomain is located in the cytoplasm before lysis of the host cell. In the otherwise re...

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