title: Flavin-induced oligomerization in Escherichia coli adaptive response protein AidB.
abstract: The process known as "adaptive response" allows Escherichia coli to respond to small doses of DNA-methylating agents by upregulating the expression of four proteins. While the role of three of these proteins in mitigating DNA damage is well understood, the function of AidB is less clear. Although AidB is a flavoprotein, no catalytic role has been established for the bound cofactor. Here we investigate the possibility that flavin plays a structural role in the assembly of the AidB tetramer. We report the generation and biophysical characterization of deflavinated AidB and of an AidB mutant that has greatly reduced affinity for flavin adenine dinucleotide (FAD). Using fluorescence quenching and analytical ultracentrifugation, we find that apo AidB has a high affinity for FAD, as indicated by an apparent dissociation constant of 402.1 ± 35.1 nM, and that binding of substoichiometric amounts of FAD triggers a transition in the AidB oligomeric state. In particular, deflavinated AidB is dimeric, whereas the addition of FAD yields a tetramer. We further investigate the dimerization and tetramerization interfaces of AidB by determining a 2.8 Å resolution crystal structure in space group P3(2) that contains three intact tetramers in the asymmetric unit. Taken together, our findings provide strong evidence that FAD plays a structural role in the formation of tetrameric AidB.
authors: Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA.
authors: Michael J
authors: MJ
authors: Hamill
authors: Marco
authors: M
authors: Jost
authors: Cintyu
authors: C
authors: Wong
authors: Sean J
authors: SJ
authors: Elliott
authors: Catherine L
authors: CL
authors: Drennan
mesh_terms: D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005415:Flavins / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D055503:Protein Multimerization
chemical_list: C090096:AidB protein, E coli; D029968:Escherichia coli Proteins; D005415:Flavins