title: Lysine residue at position 22 of the AID protein regulates its class switch activity.
abstract: BACKGROUND
  Activation induced deaminase (AID) mediates class switch recombination and somatic hypermutation of immunoglobulin (Ig) genes in germinal centre B cells. In order to regulate its specific activity and as a means to keep off-target mutations low, several mechanisms have evolved, including binding to specific cofactors, phosphorylation and destabilization of nuclear AID protein. Although ubiquitination at lysine residues of AID is recognized as an essential step in initiating degradation of nuclear AID, any functional relevance of lysine modifications has remained elusive.
  
  
  RESULTS
  Here, we report functional implications of lysine modifications of the human AID protein by generating a panel of lysine to arginine mutants of AID and assessment of their catalytic class switch activity. We found that only mutation of Lys22 to Arg resulted in a significant reduction of class switching to IgG1 in transfected primary mouse B cells. This decrease in activity was neither reflected in reduced hypermutation of Ig genes in AID-mutant transfected DT40 B cell lines nor recapitulated in bacterial deamination assays, pointing to involvement of post-translational modification of Lys22 for AID activity in B cells.
  
  
  CONCLUSIONS
  Our results imply that lysine modification may represent a novel level of AID regulation and that Lys22 is important for effective AID activity.
authors.affiliation: Laboratory for Immunological and Molecular Cancer Research, IIIrd Medical Department with Hematology, Medical Oncology, Hemostaseology, Rheumatology and Infectiology, Paracelsus Medical University Salzburg, Salzburg, Austria. r.geisberger@salk.at
authors.forename: Roland
authors.initials: R
authors.lastname: Geisberger
authors.forename: Michael
authors.initials: M
authors.lastname: Huemer
authors.forename: Franz J
authors.initials: FJ
authors.lastname: Gassner
authors.forename: Nadja
authors.initials: N
authors.lastname: Zaborsky
authors.forename: Alexander
authors.initials: A
authors.lastname: Egle
authors.forename: Richard
authors.initials: R
authors.lastname: Greil
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D001120:Arginine / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002645:Chickens; D003564:Cytidine Deaminase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D008239:Lysine / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000378:metabolism; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D050505:Mutant Proteins; D001120:Arginine; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase; D008239:Lysine