McBride Kevin M, Gazumyan Anna, Woo Eileen M, Barreto Vasco M, Robbiani Davide F, Chait Brian T, Nussenzweig Michel C
Laboratory of Molecular Immunology and Laboratory of Mass Spectrometry, The Rockefeller University and Howard Hughes Medical Institute, New York, NY 10021, USA.
Proc Natl Acad Sci U S A. 2006 Jun 6;103(23):8798-803. doi: 10.1073/pnas.0603272103. Epub 2006 May 24.
Activation-induced cytidine deaminase (AID) initiates Ig class switch recombination and somatic hypermutation by producing U:G mismatches in DNA. These mismatches also have the potential to induce DNA damage including double-stranded breaks and chromosome translocations; therefore, strict regulation of AID is important for maintaining genomic stability. In addition to transcriptional regulation, it has been proposed that phosphorylation can also modulate AID activity. Using a combination of MS and immunochemical approaches we found that 5-15% of the AID expressed in activated B cells was phosphorylated at serine-38 (p38AID). This form of AID was enriched in the chromatin fraction in activated B cells, suggesting a role for phosphorylation in targeting AID to DNA. Consistent with this idea, serine-38 to alanine mutant AID (AID(S38A)) showed diminished somatic hypermutation activity on artificial and physiological DNA targets. We conclude that a small fraction of AID is phosphorylated in activated B cells and that the modified form contributes disproportionately to hypermutation.
活化诱导的胞苷脱氨酶（AID）通过在DNA中产生U:G错配来启动免疫球蛋白类别转换重组和体细胞超突变。这些错配也有可能诱导包括双链断裂和染色体易位在内的DNA损伤；因此，严格调控AID对于维持基因组稳定性很重要。除了转录调控外，有人提出磷酸化也可以调节AID活性。我们使用质谱和免疫化学方法相结合的手段发现，活化B细胞中表达的AID有5%-15%在丝氨酸38处被磷酸化（p38AID）。这种形式的AID在活化B细胞的染色质部分中富集，表明磷酸化在将AID靶向DNA方面发挥作用。与这一观点一致的是，丝氨酸38突变为丙氨酸的突变型AID（AID(S38A)）在人工和生理性DNA靶点上的体细胞超突变活性降低。我们得出结论，活化B细胞中有一小部分AID被磷酸化，并且这种修饰形式对超突变的贡献不成比例。
