THE MULTIDIMENSIONAL CHARACTERIZATION OF AID AND AID-LIKE ENZYMES IN EARLY-EVOLVED SPECIES
Emma Quinlan, Memorial University of Newfoundland
Emma Quinlan1, Chris Amemiya2, Ellen Hsu3, Stephen Holland4, Lesley Berghuis1, Justin King1, Thomas Boehm4, and Mani Larijani1
1Department of Biomedical Sciences, Faculty of Medicine, Memorial University of NL, Canada;
2Department of Biology, University of Washington, WA, United States;
3Department of Physiology and Pharmacology, SUNY Downstate Medical Center, NY, United States; 4Max Planck Institute
of Immunobiology and Epigenetics, 79108 Freiburg, Germany
The immunoglobulin (Ig)-based adaptive immune system (AIS) evolved ~500 mya in jawed vertebrates, while the jawless vertebrates, although lacking many AIS components such as Ig, exhibit their own variable lymphocyte receptor (VLR)-based AIS. An evolutionarily-conserved hallmark of the Ig-based AIS is diversification of Ig-class antibodies through Somatic Hypermutation (SHM) and/or Class Switch Recombination (CSR) of Ig genes, which are initiated by the DNA-mutating enzyme Activation-induced cytidine deaminase (AID). The VLR-based AIS is thought to also involve activities of AID-like enzymes, the mechanisms of which remain unknown. Interestingly, while each clade of jawed vertebrate fishes possesses genetically-diverse AID, the jawless vertebrate lamprey has multiple AID-like genes, with the unique phenomenon of varying expression patterns between individuals of the same species. To understand the role of AID in AIS evolution, and to elucidate structure-function relationships in these distinct AID proteins, we structurally and biochemically examined AID from the sea and freshwater lampreys, nurse shark, zebrafish, tetraodon, coelacanth, and human. We found the defining properties of human AID were conserved across all jawed vertebrates, while other characteristics, like optimal
temperature, diverged. Furthermore, the lamprey AID orthologues exhibited varying pH sensitivities and enzyme activity levels, similar to human AID and its APOBEC relatives, suggesting unique roles for these AID orthologues in the lamprey AIS. This is the first study to biochemically and structurally characterize this number and diversity of AID and AID/APOBEClike enzymes. This multidimensional approach of multi-species in silico structural analysis and biochemical characterization exemplifies a comprehensive method for understanding enzyme evolution.
This research is supported by funds from the Canadian Institute of Health Research (CIHR), Natural Sciences and Engineering Research Council of Canada (NSERC) and Memorial University of Newfoundland.