viruses Review Insights into the Structures and Multimeric Status of APOBEC Proteins Involved in Viral Restriction and Other Cellular Functions Xiaojiang S. Chen 1,2,3 1 Molecular and Computational Biology, Departments of Biological Sciences, Chemistry, University of Southern California, Los Angeles, CA 90089, USA;
[email protected]; Tel.: +1-213-740-5487 2 Genetic, Molecular and Cellular Biology Program, Keck School of Medicine, Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA 90089, USA 3 Center of Excellence in NanoBiophysics/Structural Biology, University of Southern California, Los Angeles, CA 90089, USA Abstract: Apolipoprotein B mRNA editing catalytic polypeptide-like (APOBEC) proteins belong to a family of deaminase proteins that can catalyze the deamination of cytosine to uracil on single- stranded DNA or/and RNA. APOBEC proteins are involved in diverse biological functions, including adaptive and innate immunity, which are critical for restricting viral infection and endogenous retroelements. Dysregulation of their functions can cause undesired genomic mutations and RNA modification, leading to various associated diseases, such as hyper-IgM syndrome and cancer. This review focuses on the structural and biochemical data on the multimerization status of individual APOBECs and the associated functional implications. Many APOBECs form various multimeric complexes, and multimerization is an important way to regulate functions for some of these proteins at several levels, such as deaminase activity, protein stability, subcellular localization, protein storage Citation: Chen, X.S. Insights into and activation, virion packaging, and antiviral activity. The multimerization of some APOBECs is the Structures and Multimeric Status more complicated than others, due to the associated complex RNA binding modes.