Medicine and Health Sciences Commons^™

Complex Interplay Of Kinetic Factors Governs The Synergistic Properties Of Hiv-1 Entry Inhibitors., Koree W. Ahn, Michael J. Root

Department of Biochemistry and Molecular Biology Faculty Papers

The homotrimeric HIV-1 envelope glycoprotein (Env) undergoes receptor-triggered structural changes that mediate viral entry through membrane fusion. This process is inhibited by chemokine receptor antagonists (CoRAs) that block Env-receptor interactions and by fusion inhibitors (FIs) that disrupt Env conformational transitions. Synergy between CoRAs and FIs has been attributed to a CoRA-dependent decrease in the rate of viral membrane fusion that extends the lifetime of the intermediate state targeted by FIs. Here, we demonstrated that the magnitude of CoRA/FI synergy unexpectedly depends on FI-binding affinity and the stoichiometry of chemokine receptor binding to trimeric Env. For C-peptide FIs (clinically represented by …

Conservation Of Structure And Mechanism By Trm5 Enzymes., Thomas Christian, Howard Gamper, Ya-Ming Hou

Department of Biochemistry and Molecular Biology Faculty Papers

Enzymes of the Trm5 family catalyze methyl transfer from S-adenosyl methionine (AdoMet) to the N¹ of G37 to synthesize m¹ G37-tRNA as a critical determinant to prevent ribosome frameshift errors. Trm5 is specific to eukaryotes and archaea, and it is unrelated in evolution from the bacterial counterpart TrmD, which is a leading anti-bacterial target. The successful targeting of TrmD requires detailed information on Trm5 to avoid cross-species inhibition. However, most information on Trm5 is derived from studies of the archaeal enzyme Methanococcus jannaschii (MjTrm5), whereas little information is available for eukaryotic enzymes. Here we use human Trm5 (Homo sapiens; HsTrm5) …

Potential For Interdependent Development Of Trna Determinants For Aminoacylation And Ribosome Decoding., Cuiping Liu, Howard Gamper, Hanqing Liu, Barry S Cooperman, Ya-Ming Hou

Department of Biochemistry and Molecular Biology Faculty Papers

Although the nucleotides in tRNA required for aminoacylation are conserved in evolution, bacterial aminoacyl-transfer RNA synthetases are unable to acylate eukaryotic tRNA. The cross-species barrier may be due to the absence of eukaryote-specific domains from bacterial aminoacyl-transfer RNA synthetases. Here we show that whereas Escherichia coli CysRS cannot acylate human tRNA(Cys), the fusion of a eukaryote-specific domain of human CysRS overcomes the cross-species barrier in human tRNA(Cys). In addition to enabling recognition of the sequence differences in the tertiary core of tRNA(Cys), the fused eukaryotic domain redirects the specificity of E. coli CysRS from the A37 present in bacterial tRNA(Cys) …

Ribosome Recycling Step In Yeast Cytoplasmic Protein Synthesis Is Catalyzed By Eef3 And Atp., Shinya Kurata, Klaus H Nielsen, Sarah F Mitchell, Jon R Lorsch, Akira Kaji, Hideko Kaji

Department of Biochemistry and Molecular Biology Faculty Papers

After each round of protein biosynthesis, the posttermination complex (PoTC) consisting of a ribosome, mRNA, and tRNA must be disassembled into its components for a new round of translation. Here, we show that a Saccharomyces cerevisiae model PoTC was disassembled by ATP and eukaryotic elongation factor 3 (eEF3). GTP or ITP functioned with less efficiency and adenosine 5gamma'-(beta,gamma-imido)triphosphate did not function at all. The k(cat) of eEF3 was 1.12 min(-1), which is comparable to that of the in vitro initiation step. The disassembly reaction was inhibited by aminoglycosides and cycloheximide. The subunits formed from the yeast model PoTC remained separated …

Asymmetric Deactivation Of Hiv-1 Gp41 Following Fusion Inhibitor Binding., Kristen M Kahle, H Kirby Steger, Michael J Root

Department of Biochemistry and Molecular Biology Faculty Papers

Both equilibrium and nonequilibrium factors influence the efficacy of pharmaceutical agents that target intermediate states of biochemical reactions. We explored the intermediate state inhibition of gp41, part of the HIV-1 envelope glycoprotein complex (Env) that promotes viral entry through membrane fusion. This process involves a series of gp41 conformational changes coordinated by Env interactions with cellular CD4 and a chemokine receptor. In a kinetic window between CD4 binding and membrane fusion, the N- and C-terminal regions of the gp41 ectodomain become transiently susceptible to inhibitors that disrupt Env structural transitions. In this study, we sought to identify kinetic parameters that …

The Role Of Gtp In Transient Splitting Of 70s Ribosomes By Rrf (Ribosome Recycling Factor) And Ef-G (Elongation Factor G)., Go Hirokawa, Nobuhiro Iwakura, Akira Kaji, Hideko Kaji

Department of Biochemistry and Molecular Biology Faculty Papers

Ribosome recycling factor (RRF), elongation factor G (EF-G) and GTP split 70S ribosomes into subunits. Here, we demonstrated that the splitting was transient and the exhaustion of GTP resulted in re-association of the split subunits into 70S ribosomes unless IF3 (initiation factor 3) was present. However, the splitting was observed with sucrose density gradient centrifugation (SDGC) without IF3 if RRF, EF-G and GTP were present in the SDGC buffer. The splitting of 70S ribosomes causes the decrease of light scattering by ribosomes. Kinetic constants obtained from the light scattering studies are sufficient to account for the splitting of 70S ribosomes …

Neutralization Of Botulinum Neurotoxin By A Human Monoclonal Antibody Specific For The Catalytic Light Chain., Sharad P Adekar, Tsuyoshi Takahashi, R Mark Jones, Fetweh H Al-Saleem, Denise M Ancharski, Michael J Root, B P Kapadnis, Lance L Simpson, Scott K Dessain

Department of Biochemistry and Molecular Biology Faculty Papers

BACKGROUND: Botulinum neurotoxins (BoNT) are a family of category A select bioterror agents and the most potent biological toxins known. Cloned antibody therapeutics hold considerable promise as BoNT therapeutics, but the therapeutic utility of antibodies that bind the BoNT light chain domain (LC), a metalloprotease that functions in the cytosol of cholinergic neurons, has not been thoroughly explored.

METHODS AND FINDINGS: We used an optimized hybridoma method to clone a fully human antibody specific for the LC of serotype A BoNT (BoNT/A). The 4LCA antibody demonstrated potent in vivo neutralization when administered alone and collaborated with an antibody specific for …

Anti-Human Immunodeficiency Virus (Hiv) Activities Of Halogenated Gomisin J Derivatives, New Nonnucleoside Inhibitors Of Hiv Type 1 Reverse Transcriptase, Toshiaki Fujihashi, Hiroto Hara, Toshiya Sakata, Kazuya Mori, Hirotaka Higuchi, Akio Tanaka, Hideko Kaji, Akira Kaji

Department of Biochemistry and Molecular Biology Faculty Papers

Halogenated gomisin J (a derivative of lignan compound), represented by the bromine derivative 1506 [(6R, 7S, S-biar)-4,9-dibromo-3,10-dihydroxy-1,2,11,12-tetramethoxy-6, 7-dimethyl-5,6,7,8- tetrahydrodibenzo[a,c]cyclo-octene], was found to be a potent inhibitor of the cytopathic effects of human immunodeficiency virus type 1 (HIV-1) on MT-4 human T cells (50% effective dose, 0.1 to 0.5 microM). Gomisin J derivatives were active in preventing p24 production from acutely HIV-1-infected H9 cells. The selective indices (toxic dose/effective dose) of these compounds were as high as > 300 in some systems. 1506 was active against 3'-azido-3'-deoxythymidine-resistant HIV-1 and acted synergistically with AZT and 2',3'-ddC. 1506 inhibited HIV-1 reverse transcriptase (RT) in …