The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein complex (gp120-gp41) promotes viral entry by mediating the fusion of viral and cellular membranes. Formation of a stable trimer-of-hairpins structure in the gp41 ectodomain brings the two membranes into proximity, leading to membrane fusion. The core of this hairpin structure is a six-helix bundle in which three carboxylterminal outer helices pack against an inner trimeric coiled coil. Here we investigate the role of these conserved interhelical interactions on the structure and function of both the envelope glycoprotein and the gp41 core. We have replaced each of the eight amino acids at the buried face of the carboxyl-terminal helix with a representative amino acid, alanine. Structural and physicochemical characterization of the alanine mutants shows that hydrophobic interactions are a dominant factor in the stabilization of the six-helix bundle. Alanine substitutions at the Trp628, Trp631, Ile635, and Ile642 residues also affected envelope processing and/or gp120-gp41 association and abrogated the ability of the envelope glycoprotein to mediate cell-cell fusion. These results suggest that the amino-terminal region of the gp41 outer-layer R-helix plays a key role in the sequence of events associated with HIV-1 entry and have implications for the development of antibodies and small-molecule inhibitors of this conserved element.

The human and simian immunodeficiency viruses (HIV and SIV) envelope glycoprotein consists of a trimer of two noncovalently and weakly associated subunits, gp120 and gp41. Upon binding of gp120 to cellular receptors, this labile native envelope complex undergoes conformational changes, resulting in a stable trimer-of-hairpins structure in gp41. Formation of the hairpin structure is thought to mediate membrane fusion by placing the viral and cellular membranes in close proximity. An in-vitro-derived variant of SIVmac251, denoted CPmac, has acquired an unusually stable virion-associated gp120-gp41 complex. This unique phenotype is conferred by five amino-acid substitutions in the gp41 ectodomain. Here we characterize the structural and physicochemical properties of the N40(L6)C38 model of the CPmac gp41 core. The 1.7

运用激光光解与脉冲辐解技术，对用于肿瘤治疗的鬼臼毒素（PPT）和依托泊试（VP-16）的化学活性进行了详细的研究结果表明鬼臼毒素及（VP-16）经248nm的激光激发可光电离，且光电离的量子产额比较高，有很强的光敏性，而且还有多个活性基团分别与水合电子、氢原子、经基自由基作用生成不同的瞬态粒子，并推断出相应的反应机理为医学工作者进一步了解、利用鬼臼毒素和VP-16，探讨其抗肿瘤机理提供科学的参考，也为化学工作者进一步合成高效、低毒的抗肿瘤药物提供新思路。

Membrane fusion by human immunodeficiency virus type 1 (HIV-1) is promoted by the refolding of the viral envelope glycoprotein into a fusion-active conformation. The structure of the gp41 ectodomain core in its fusion-active state is a trimer of hairpins in which three antiparallel carboxyl-terminal helices pack into hydrophobic grooves on the surface of an amino-terminal trimeric coiled coil. In an effort to identify amino acid residues in these grooves that are critical for gp41 activation, we have used alanine-scanning mutagenesis to investigate the importance of individual side chains in determining the biophysical properties of the gp41 core and the membrane fusion activity of the gp120-gp41 complex. Alanine substitutions at Leu-556, Leu-565, Val-570, Gly-572, and Arg-579 positions severely impaired membrane fusion activity in envelope glycoproteins that were for the most part normally expressed. Whereas alanine mutations at Leu-565 and Val-570 destabilized the trimer-of-hairpins structure, mutations at Gly-572 and Arg-579 led to the formation of a stable gp41 core. Our results suggest that the Leu-565 and Val-570 residues are important determinants of conserved packing interactions between the amino- and carboxyl-terminal helices of gp41. We propose that the high degree of sequence conservation at Gly-572 and Arg-579 may result from selective pressures imposed by prefusogenic conformations of the HIV-1 envelope glycoprotein. Further analysis of the gp41 activation process may elucidate targets for antiviral intervention.

分析了鬼臼毒素及其衍生物与还原性自由基（氢自由基、水合电子）作用、氧化性自由基羟基自由基和激光等作用后产生的各种瞬态粒子，对各粒子的生成和衰减过程进行跟踪，获得了各瞬态粒子的生成和衰减速率常数，进一步探讨了鬼臼毒素治疗肿瘤的构效关系。