Despite the remarkable success of combination antiretroviral therapy, HIV-1 remains among the major causes of human suffering and loss of life in poor and developing nations. To prevail in this drawn-out battle with the pandemic, it is essential to continue developing advanced antiviral agents to fight drug resistant HIV-1 variants.

In this study, we generated mice lacking the gene for G-substrate, a specific substrate for cGMP-dependent protein kinase uniquely located in cerebellar Purkinje cells, and explored their specific functional deficits. G-substrate-deficient Purkinje cells in slices obtained at postnatal weeks (PWs) 10 -15 maintained electrophysiological properties essentially similar to those from WT littermates. Conjunction of parallel fiber stimulation and depolarizing pulses induced long-term depression (LTD) normally. At younger ages, however, LTD attenuated temporarily at PW6 and recovered thereafter. In parallel with LTD, short-term (1 h) adaptation of optokinetic eye movement response (OKR) temporarily diminished at PW6. Young adult G-substrate knockout mice tested at PW12 exhibited no significant differences from their WT littermates in terms of brain structure, general behavior, locomotor behavior on a rotor rod or treadmill, eyeblink conditioning, dynamic characteristics of OKR, or short-term OKR adaptation. One unique change detected was a modest but significant attenuation in the long-term (5 days) adaptation of OKR. The present results support the concept that LTD is causal to short-term adaptation and reveal the dual functional involvement of G-substrate in neuronal mechanisms of the cerebellum for both short-term and long-term adaptation.cerebellum ͉ long-term depression ͉ optokinetic response ͉ Purkinje cell

In addition to its catalytic function, HIV-1 integrase (IN) binds to the viral RNA genome (gRNA) through positively charged residues (i.e., R262, R263, R269, K273) within its C-terminal domain (CTD) and regulates proper virion maturation. Mutation of these residues results in the formation of morphologically aberrant viruses blocked at an early reverse transcription stage in cells.

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Independent of its catalytic activity, HIV-1 integrase (IN) enzyme regulates proper particle maturation by binding to and packaging the viral RNA genome (gRNA) inside the mature capsid lattice. Allosteric integrase inhibitors (ALLINIs) and class II IN substitutions inhibit the binding of IN to the gRNA and cause the formation of non-infectious virions characterized by mislocalization of the viral ribonucleoprotein complexes between the translucent conical capsid lattice and the viral lipid envelope. To gain insight into the molecular nature of IN-gRNA interactions, we have isolated compensatory substitutions in the background of a class II IN (R269A/K273A) variant that directly inhibits IN binding to the gRNA. We found that additional D256N and D270N substitutions in the C-terminal domain (CTD) of IN restored its ability to bind gRNA and led to the formation of infectious particles with correctly matured morphology. Furthermore, reinstating the overall positive electrostatic potential of the CTD through individual D256R or D256K substitutions was sufficient to restore IN-RNA binding and infectivity for the R269A/K273A as well as the R262A/R263A class II IN mutants. The compensatory mutations did not impact functional IN oligomerization, suggesting that they directly contributed to IN binding to the gRNA. Interestingly, HIV-1 IN R269A/K273A, but not IN R262A/R263A, bearing compensatory mutations was more sensitive to ALLINIs providing key genetic evidence that specific IN residues required for RNA binding also influence ALLINI activity. Structural modeling provided further insight into the molecular nature of IN-gRNA interactions and ALLINI mechanism of action. Taken together, our findings highlight an essential role of IN-gRNA interactions for proper virion maturation and reveal the importance of electrostatic interactions between the IN CTD and the gRNA.AUTHOR SUMMARYIn addition to its well-defined catalytic function, HIV-1 integrase (IN) binds to the viral RNA genome and regulates proper virion maturation. Inhibition of IN binding to the HIV-1 genome through mutations of positively charged residues within the C-terminal domain (CTD, i.e. R269, K273) results in non-infectious particles in which the viral genomes are mislocalized in improperly matured virions. Here we have isolated compensatory mutations in the background of the class II IN (R269A/K273A) mutant virus that restored the ability of IN to bind RNA. We found that additional substitutions of nearby acidic residues (i.e. D256 and D270), which restored the overall positive charge of the CTD, rescued the ability of IN to bind RNA and thus resulted in formation of correctly matured, infectious virions. These compensatory substitutions also revealed the role of specific residues within the CTD that determine sensitivity to allosteric integrase inhibitors (ALLINIs), a class of compounds that indirectly target IN-RNA interactions. Taken together, our findings reveal the importance of the electrostatic interactions between the IN CTD and the gRNA and provide key genetic evidence for a crucial role of the CTD in antiviral activity of ALLINIs.

Three-dimensional structures of I86A and C295A mutant secondary alcohol dehydrogenase (SADH) from Thermoanaerobacter pseudoethanolicus were determined byx-ray crystallography. The tetrameric structure of C295A-SADH soaked with NADP + and dimethyl sulfoxide (DMSO) was determined to 1.85 Å with an R free of 0.225.DMSO is bound to the tetrahedral zinc in each subunit, with ligands from SG of Cys-37, NE2 of His-59, and OD2 of Asp-150. The nicotinamide ring of NADP is hydrogen-bonded to the N of Ala-295 and the O of Val-265 and Gly-293. The O of DMSO is connected to a network of hydrogen bonds with OG of Ser-39, the 3 0 -OH of NADP, and ND1 of His-42. The structure of I86A-SADH soaked with 2-pentanol and NADP + contains (R)-2-pentanol bound in each subunit, ligated to the tetrahedral zinc, and connected to the proton relay network. The structure of I86A-SADH soaked with 3-methylcyclohexanol and NADP + has alcohol bound in three subunits.Two of the sites have the alcohol ligated to the zinc in an axial position, with OE2 of Glu-60 in the other axial position of a trigonal bipyramidal complex. One site has 3-methylcyclohexanol bound noncovalently, with the zinc in an inverted tetrahedral geometry with Glu-60. The fourth site also has the zinc in a trigonal bipyramidal complex with axial Glu-60 and water ligands. These structures demonstrate that ligand exchange of SADH involves pentacoordinate and inverted zinc complexes with Glu-60. Furthermore, we see a network of hydrogen bonds connecting the substrate oxygen to the external solvent that is likely to play a role in the mechanism of SADH.enzyme mechanism, pentacoordinate zinc, stereospecificity, tetrahedral zinc, zinc complex | INTRODUCTIONAlcohol dehydrogenases are valuable catalysts for the asymmetric reduction of ketones to produce chiral alcohols. The thermostable secondary alcohol dehydrogenases (SADH) from Thermoanaerobacter brockii and Thermoanaerobacter (pseudo) ethanolicus have been extensively used for this purpose. [1][2][3] The enzymes from these two bacterial sources have been shown recently to have an identical amino acid sequence. 2 This enzyme is a member of the medium-chain dehydrogenase/reductases (MDRs) family. Similar to other MDRs, each chain of SADH contains 352 amino acid residues. However, it shares only 27% sequence identity with the more widely studied horse liver alcohol dehydrogenase (HLADH). Because of its potential application in chiral syntheses, there have been numerous studies to broaden the