Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.5.1.4 (deaminase)
5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human APOBEC3G exhibits anti-human immunodeficiency virus-1 (HIV-1) activity by deaminating cytidines of the minus strand of HIV-1. Here, we report a solution structure of the C-terminal deaminase domain of wild-type APOBEC3G. The interaction with DNA was examined. Many differences in the interaction were found between the wild type and recently studied mutant APOBEC3Gs. The position of the substrate cytidine, together with that of a DNA chain, in the complex, was deduced. Interestingly, the deamination reaction of APOBEC3G was successfully monitored using NMR signals in real time. Real-time monitoring has revealed that the third cytidine of the d(CCCA) segment is deaminated at an early stage and that then the second one is deaminated at a late stage, the first one not being deaminated at all. This indicates that the deamination is carried out in a strict 3' --> 5' order. Virus infectivity factor (Vif) of HIV-1 counteracts the anti-HIV-1 activity of APOBEC3G. The structure of the N-terminal domain of APOBEC3G, with which Vif interacts, was constructed with homology modelling. The structure implies the mechanism of species-specific sensitivity of APOBEC3G to Vif action.
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PMID:Structure, interaction and real-time monitoring of the enzymatic reaction of wild-type APOBEC3G. 1915 9

Cytidine deamination is the primary mechanism by which APOBEC3G restricts HIV-1; however, several studies have reported that APOBEC3G also inhibits virus replication via a mechanism that is independent of deamination. Using active site APOBEC3G mutants, we have re-evaluated the biological relevance of deaminase-independent APOBEC3G-mediated restriction of HIV-1. APOBEC3G proteins with Glu-->Ala mutations in AS1, AS2 or AS1 and AS2 were stably expressed at physiological levels in CEM-SS T cells and 293T cells and the ability of the cells to support Deltavif HIV-1 replication was then tested. The AS2 and AS1/AS2 mutants were packaged efficiently into virions but in single-cycle or multi-cycle HIV-1 replication assays, were found to lack antiviral activity. The AS1 mutant, which retained deaminase activity, maintained near wild-type antiviral function. To determine the potency of APOBEC3G antiviral activity, cell lines were established that that expressed low levels of wild-type APOBEC3G and generated virions that contained as few as 1-2 APOBEC3G molecules. Even at very low copy number, APOBEC3G caused a significant reduction in infectivity, suggesting that a single molecule of packaged APOBEC3G inactivates the virus. The high potency of APOBEC3G is consistent with a catalytic mechanism of restriction in which a single molecule can induce a string of mutations but difficult to reconcile with a deaminase-independent, non-catalytic mechanism. Analysis of the reverse transcript sequences showed that the G-->A mutations were clustered, likely reflecting the action of single APOBEC3G molecules acting processively. We conclude that cytidine deamination is the mechanism by which APOBEC3G restricts HIV-1.
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PMID:Restriction of HIV-1 by APOBEC3G is cytidine deaminase-dependent. 1930 4

The APOBEC3 proteins form a multigene family of cytidine deaminases with inhibitory activity against viruses and retrotransposons. In contrast to APOBEC3G (A3G), APOBEC3A (A3A) has no effect on lentiviruses but dramatically inhibits replication of the parvovirus adeno-associated virus (AAV). To study the contribution of deaminase activity to the antiviral activity of A3A, we performed a comprehensive mutational analysis of A3A. By mutation of non-conserved residues, we found that regions outside of the catalytic active site contribute to both deaminase and antiviral activities. Using A3A point mutants and A3A/A3G chimeras, we show that deaminase activity is not required for inhibition of recombinant AAV production. We also found that deaminase-deficient A3A mutants block replication of both wild-type AAV and the autonomous parvovirus minute virus of mice (MVM). In addition, we identify specific residues of A3A that confer activity against AAV when substituted into A3G. In summary, our results demonstrate that deaminase activity is not necessary for the antiviral activity of A3A against parvoviruses.
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PMID:Deaminase-independent inhibition of parvoviruses by the APOBEC3A cytidine deaminase. 1946 82

The innate antiviral factor APOBEC3G (A3G) possesses RNA binding activity and deaminates HIV-1 DNA. High-molecular mass forms of A3G can be isolated from a variety of cell types but exhibit limited deaminase activity relative to low-molecular mass species prepared under RNA-depleted conditions. To investigate the fundamental oligomeric state and shape of A3G, we conducted sedimentation velocity analyses of the pure enzyme under RNA-deficient conditions. The results reveal a predominant dimer in equilibrium with minor monomeric and tetrameric species. Hydrodynamic modeling of the dimer supports an extended cylindrical shape that assembles into an elongated tetramer. Overall, the results provide physical restraints for the A3G quaternary structure that have implications for modulating antiviral function.
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PMID:A hydrodynamic analysis of APOBEC3G reveals a monomer-dimer-tetramer self-association that has implications for anti-HIV function. 1983 47

Inhibition of the interaction of the human cytidine-deaminase APOBEC3G (A3G) with the human immunodeficiency virus (HIV) type 1-specific viral infectivity factor (Vif) represents a novel therapeutic approach in which a cellular factor with potent antiviral activity (A3G) plays a key role. In HIV-infected cells, the interaction of Vif with A3G leads to the subsequent degradation of A3G by the 26S proteasome via the ubiquitin pathway and to the loss of antiviral activity. To establish a stable and convenient cellular testing platform for the high-throughput screening of potential antiviral compound libraries, we engineered a double transgenic cell line constitutively expressing an enhanced yellow fluorescent protein expressor (EYFP-A3G) fusion as well as a Tet-Off controllable Vif protein. With this cell line, we were able to measure precisely the Vif-induced degradation of A3G in the presence of potential antiviral compounds in an easy-to-handle, robust, and practical high-throughput multiwell plate format with an excellent screening window coefficient (Z factor) of 0.67.
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PMID:Inducible APOBEC3G-Vif double stable cell line as a high-throughput screening platform to identify antiviral compounds. 1984 Nov 53

Recently, conflicting results were reported on the hypermutation activity of activation-induced cytidine deaminase (AID) splice variants. With the generation of single point mutations, we studied the structure-function relationship of the amino acids that are commonly absent from all described splice variants. The results from this analysis pointed to several amino acids that are required for class switch recombination (CSR), without perturbing cellular localization or nucleocytoplasmic shuttling. A defect in deaminase activity was found to underlie this CSR deficiency. Interestingly, the most debilitating mutations concentrated on hydrophobic amino acids, suggesting a structural role for this part of the protein. Indeed, by generating homologous amino acid replacements, CSR activity could be restored. These results are in agreement with recent reports on the protein structure of the AID homolog APOBEC3G, suggesting a similar protein composition. In addition, the findings underscore that AID splice variants are unlikely to have preservation of catalytic activity.
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PMID:Activation-induced cytidine deaminase splice variants are defective because of the lack of structural support for the catalytic site. 2011 83

APOBEC3G is a DNA cytidine deaminase that has antiviral activity against HIV-1 and other pathogenic viruses. In this study the crystal structure of the catalytically active C-terminal domain was determined to 2.25 A. This structure corroborates features previously observed in nuclear magnetic resonance (NMR) studies, a bulge in the second beta strand and a lengthening of the second alpha helix. Oligomerization is postulated to be critical for the function of APOBEC3G. In this structure, four extensive intermolecular interfaces are observed, suggesting potential models for APOBEC3G oligomerization. The structural and functional significance of these interfaces was probed by solution NMR and disruptive variants were designed and tested for DNA deaminase and anti-HIV activities. The variant designed to disrupt the most extensive interface lost both activities. NMR solution data provides evidence that another interface, which coordinates a novel zinc site, also exists. Thus, the observed crystallographic interfaces of APOBEC3G may be important for both oligomerization and function.
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PMID:Crystal structure of the APOBEC3G catalytic domain reveals potential oligomerization interfaces. 2015 50

At least two human APOBEC3 proteins - APOBEC3F and APOBEC3G - are capable of inhibiting HIV-1 replication by mutation of the viral cDNA. HIV-1 averts lethal restriction through its accessory protein Vif, which targets these APOBEC3 proteins for proteasomal degradation. The life-or-death interaction between human APOBEC3 proteins and HIV-1 Vif has stimulated much interest in developing novel therapeutics aimed at altering the deaminase activity of the APOBEC3s, thus changing the virus' mutation rate to either lethal or suboptimal levels. The current state of mechanistic information is reviewed and the possible risks and benefits of increasing (via hypermutation) or decreasing (via hypomutation) the HIV-1 mutation rate through APOBEC3 proteins are discussed.
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PMID:Leveraging APOBEC3 proteins to alter the HIV mutation rate and combat AIDS. 2017 54

In HIV-1-infected individuals, G-to-A hypermutation is found in HIV-1 DNA isolated from peripheral blood mononuclear cells (PBMCs). These mutations are thought to result from editing by one or more host enzymes in the APOBEC3 (A3) family of cytidine deaminases, which act on CC (APOBEC3G) and TC (other A3 proteins) dinucleotide motifs in DNA (edited cytidine underlined). Although many A3 proteins display high levels of deaminase activity in model systems, only low levels of A3 deaminase activity have been found in primary cells examined to date. In contrast, here we report high levels of deaminase activity at TC motifs when whole PBMCs or isolated primary monocyte-derived cells were treated with interferon-alpha (IFNalpha) or IFNalpha-inducing toll-like receptor ligands. Induction of TC-specific deaminase activity required new transcription and translation and correlated with the appearance of two APOBEC3A (A3A) isoforms. Knockdown of A3A in monocytes with siRNA abolished TC-specific deaminase activity, confirming that A3A isoforms are responsible for all TC-specific deaminase activity observed. Both A3A isoforms appear to be enzymatically active; moreover, our mutational studies raise the possibility that the smaller isoform results from internal translational initiation. In contrast to the high levels of TC-specific activity observed in IFNalpha-treated monocytes, CC-specific activity remained low in PBMCs, suggesting that A3G deaminase activity is relatively inhibited, unlike that of A3A. Together, these findings suggest that deaminase activity of A3A isoforms in monocytes and macrophages may play an important role in host defense against viruses.
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PMID:Innate immune signaling induces high levels of TC-specific deaminase activity in primary monocyte-derived cells through expression of APOBEC3A isoforms. 2061 67

Mouse APOBEC3 (mA3) is a cytidine deaminase with antiviral activity. mA3 is linked to the Rfv3 virus resistance factor, a gene responsible for recovery from infection by Friend murine leukemia virus, and mA3 allelic variants differ in their ability to restrict mouse mammary tumor virus. We sequenced mA3 genes from 38 inbred strains and wild mouse species, and compared the mouse sequence and predicted structure with human APOBEC3G (hA3G). An inserted sequence was identified in the virus restrictive C57BL strain allele that disrupts a splice donor site. This insertion represents the long terminal repeat of the xenotropic mouse gammaretrovirus, and was acquired in Eurasian mice that harbor xenotropic retrovirus. This viral regulatory sequence does not alter splicing but is associated with elevated mA3 expression levels in spleens of laboratory and wild-derived mice. Analysis of Mus mA3 coding sequences produced evidence of positive selection and identified 10 codons with very high posterior probabilities of having evolved under positive selection. Six of these codons lie in two clusters in the N-terminal catalytically active cytidine deaminase domain (CDA), and 5 of those 6 codons are polymorphic in Rfv3 virus restrictive and nonrestrictive mice and align with hA3G CDA codons that are critical for deaminase activity. Homology models of mA3 indicate that the two selected codon clusters specify residues that are opposite each other along the predicted CDA active site groove, and that one cluster corresponds to an hAPOBEC substrate recognition loop. Substitutions at these clustered mA3 codons alter antiviral activity. This analysis suggests that mA3 has been under positive selection throughout Mus evolution, and identified an inserted retroviral regulatory sequence associated with enhanced expression in virus resistant mice and specific residues that modulate antiviral activity.
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PMID:Adaptive evolution of Mus Apobec3 includes retroviral insertion and positive selection at two clusters of residues flanking the substrate groove. 2061 65


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