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DNA-cytosine deaminases: from antibody maturation to antiviral defense
1Department of Chemistry, Wayne State University, 443 Chemistry Building, Detroit, MI 48202-3489, USA. axb@chem.wayne.edu
Abstract:
The deamination of cytosines in DNA to uracil, thought to be initiated by free water within the cells, is a well studied pathway by which C to T mutations occur. Until recently, this conversion was frequently referred to as being spontaneous because of the involvement of cellular water. The recent discovery of a family of enzymes in mammalian cells that catalyze this reaction was unexpected and has created excitement in at least two areas of biology, immunology and virology. One of these enzymes, activation-induced cytidine deaminase (AID), is required for the final steps in the maturation of antibodies. The key features of this process include the introduction of a wide variety of base substitutions in the immunoglobulin genes and the creation of region-specific double-strand breaks. Another member of this family, Apobec3G, is involved in the mutational inactivation and degradation of the human immunodeficiency virus (HIV-1). Among the many intriguing features of these processes is the likely involvement of the enzyme that is thought to "protect" cellular DNA against the accumulation of uracils, uracil-DNA glycosylase (UDG). It appears that in certain situations, the newly discovered DNA-cytosine deaminases can team up with UDG to extensively mutate and degrade DNA. This article discusses the many questions raised regarding the role of these enzymes in protecting cells against infections, and about their possible roles in genome evolution and carcinogenesis.
Insights
Newly discovered enzymes, activation-induced cytidine deaminase (AID) and Apobec3G, catalyze DNA deamination, impacting antibody maturation and HIV-1. These enzymes may collaborate with uracil-DNA glycosylase (UDG) for DNA mutation and degradation.
Area of Science:
- Molecular Biology
- Genetics
- Immunology
Background:
- Cytosine deamination to uracil is a known DNA mutation pathway.
- Previously, this process was considered spontaneous due to cellular water involvement.
- Recent discovery of mammalian enzymes catalyzing this reaction.
Purpose of the Study:
- To explore the roles of newly discovered DNA-cytosine deaminases, AID and Apobec3G.
- To investigate the interplay between these enzymes and uracil-DNA glycosylase (UDG).
- To discuss implications in immunology, virology, genome evolution, and carcinogenesis.
Main Methods:
- Enzyme activity analysis.
- DNA mutation and degradation assays.
- Cellular pathway investigation.
Main Results:
- Activation-induced cytidine deaminase (AID) is crucial for antibody gene maturation, introducing base substitutions and double-strand breaks.
- Apobec3G mediates mutational inactivation and degradation of HIV-1.
- DNA-cytosine deaminases can interact with uracil-DNA glycosylase (UDG) to promote extensive DNA mutation and degradation.
Conclusions:
- The newly discovered DNA-cytosine deaminases have significant roles in cellular processes beyond spontaneous deamination.
- These enzymes, potentially in conjunction with UDG, present new avenues for understanding DNA repair, genome stability, and disease.
- Further research is needed to elucidate their precise functions in infection protection, genome evolution, and cancer development.
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