title: Biochemical Characterization of APOBEC3H Variants: Implications for Their HIV-1 Restriction Activity and mC Modification.
abstract: APOBEC3H (A3H) is the most polymorphic member of the APOBEC3 family. Seven haplotypes (hap I-VII) and four mRNA splicing variants (SV) of A3H have been identified. The various haplotypes differ in anti-HIV activity, which is attributed to differences in protein stability, subcellular distribution, and/or RNA binding and virion packaging. Here, we report the first comparative biochemical studies of all the A3H variants using highly purified proteins. We show that all haplotypes were stably expressed and could be purified to homogeneity by Escherichia coli expression. Surprisingly, four out of the seven haplotypes showed high cytosine (C) deaminase activity, with hap V displaying extremely high activity that was comparable to the highly active A3A. Furthermore, all four haplotypes that were active in C deamination were also highly active on methylated C (mC), with hap II displaying almost equal deamination efficiency on both. The deamination activity of these A3H variants correlates well with their reported anti-HIV activity for the different haplotypes, suggesting that deaminase activity may be an important factor in determining their respective anti-HIV activities. Moreover, mC deamination of A3H displayed a strong preference for the sequence motif of T-mCpG-C/G, which may suggest a potential role in genomic mC modification at the characteristic "CpG" island motif.
authors.affiliation: Molecular and Computational Biology Program, Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Jiang
authors.initials: J
authors.lastname: Gu
authors.affiliation: Molecular and Computational Biology Program, Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Qihan
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Molecular and Computational Biology Program, Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089, USA; Genetic, Molecular and Cellular Biology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Xiao
authors.initials: X
authors.lastname: Xiao
authors.affiliation: Molecular and Computational Biology Program, Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Ito
authors.affiliation: Molecular and Computational Biology Program, Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089, USA; Genetic, Molecular and Cellular Biology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Aaron
authors.initials: A
authors.lastname: Wolfe
authors.affiliation: Molecular and Computational Biology Program, Departments of Biological Sciences and Chemistry, University of Southern California, Los Angeles, CA 90089, USA; Center of Excellence in NanoBiophysics, University of Southern California, Los Angeles, CA 90089, USA; Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA 90089, USA; Genetic, Molecular and Cellular Biology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA. Electronic address: xiaojiac@usc.edu.
authors.forename: Xiaojiang S
authors.initials: XS
authors.lastname: Chen
mesh_terms: D000619:Aminohydrolases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D000998:Antiviral Agents / Q000302:isolation & purification / Q000378:metabolism*; D043525:Cytosine Deaminase / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015497:HIV-1 / Q000254:growth & development* / Q000276:immunology*; D006239:Haplotypes; D006801:Humans; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D011994:Recombinant Proteins; C529313:APOBEC3H protein, human; D000619:Aminohydrolases; D043525:Cytosine Deaminase
keywords: comparative in vitro functional studies; expression/purification of all APOBEC3H variants; mC deamination activity for mCpG; mC selectivity factor