title: Dual Role of a Biosynthetic Enzyme, CysK, in Contact Dependent Growth Inhibition in Bacteria.
abstract: Contact dependent growth inhibition (CDI) is the phenomenon where CDI+ bacterial strain (inhibitor) inhibits the growth of CDI-strain (target) by direct cell to cell contact. CDI is mediated by cdiBAI gene cluster where CdiB facilitates the export of CdiA, an exotoxin, on the cell surface and CdiI acts as an immunity protein to protect CDI+ cells from autoinhibition. CdiA-CT, the C-terminal region of the toxin CdiA, from uropathogenic Escherichia coli strain 536 (UPEC536) is a latent tRNase that requires binding of a biosynthetic enzyme CysK (O-acetylserine sulfyhydrylase) for activation in the target cells. CdiA-CT can also interact simultaneously with CysK and immunity protein, CdiI, to form a ternary complex in UPEC536. But the role of CysK in the ternary complex is not clear. We studied the hydrodynamic, thermodynamic and kinetic parameters of binary and ternary complexes using AUC, ITC and SPR respectively, to investigate the role of CysK in UPEC536. We report that CdiA-CT binds CdiI and CysK with nanomolar range affinity. We further report that binding of CysK to CdiA-CT improves its affinity towards CdiI by ~40 fold resulting in the formation of a more stable complex with over ~130 fold decrease in dissociation rate. Thermal melting experiments also suggest the role of CysK in stabilizing CdiA-CT/CdiI complex as Tm of the binary complex shifts ~10°C upon binding CysK. Hence, CysK acts a modulator of CdiA-CT/CdiI interactions by stabilizing CdiA-CT/CdiI complex and may play a crucial role in preventing autoinhibition in UPEC536. This study reports a new moonlighting function of a biosynthetic enzyme, CysK, as a modulator of toxin/immunity interactions in UPEC536 inhibitor cells.
authors.affiliation: Structural Biology Laboratory, G. N. Ramachandran Protein Centre, Council of Scientific and Industrial Research-Institute of Microbial Technology, Chandigarh, India.
authors.forename: Soni
authors.initials: S
authors.lastname: Kaundal
authors.affiliation: Structural Biology Laboratory, G. N. Ramachandran Protein Centre, Council of Scientific and Industrial Research-Institute of Microbial Technology, Chandigarh, India.
authors.forename: Manju
authors.initials: M
authors.lastname: Uttam
authors.affiliation: Structural Biology Laboratory, G. N. Ramachandran Protein Centre, Council of Scientific and Industrial Research-Institute of Microbial Technology, Chandigarh, India.
authors.forename: Krishan Gopal
authors.initials: KG
authors.lastname: Thakur
mesh_terms: D003547:Cysteine Synthase / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D053038:Quorum Sensing
chemical_list: C503242:CdiA protein, E coli; C513104:CdiB protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D003547:Cysteine Synthase