Description:
SpdE, a novel amino acid-sensing diguanylate cyclase
Tech ID UO-19-33
Animals are colonized by dynamic communities of bacteria, largely acquired by transmission from the external environment and other hosts; however, the traits that promote a microbe’s ability to be host-associated (i.e. to colonize or otherwise exist within a host) are not fully understood. We used the zebrafish as a tractable host-microbe model system to investigate how a zebrafish gut isolate, Aeromonas veronii (Aer01), increases its ability to be host associated.
From this bacteria, the researchers discovered a novel bacterial protein that senses specific amino acids. This transmembrane protein contains a diguanylate cyclase domain coupled to a small molecule-sensing PAS domain; thus, the researchers named it spdE (signaling PAS diguanylate cyclase enzyme). Using the purified PAS domain and a thermal stability assay, researchers identified several candidate ligands — hydrophobic amino acids. Excitingly, these ligands regulate SpdE’s diguanylate cyclase activity in Aer01 cultures resulting in decreased intracellular levels of cyclic di-GMP, and increased bacterial motility. In the context of the zebrafish, these amino acids both increase immigration into the host and modulate competition outcome between the wild type and spdE strains. Combined, this work contributes important insights into the selective forces in host-microbe systems and provides a specific mechanism of increased host association by a bacterial symbiont.
There are several potential applications for spdE, the amino-acid sensing protein. There are few proteins or reagents on the market that can sense amino acids at very low concentrations, and spdE can bind specific amino acids (valine, proline, and isoleucine) down to nanomolar quantities. This protein:
- Could be coupled to various enzymatic proteins or reporter proteins in order to detect these amino acids, or degrade them; this could be clinically relevant for various diseases related to metabolic amino acid disorder.
- Reporter fusions could be used to detect these amino acids in tissues, within cells or patient samples.
- Could be engineered to alter its specificity to different amino acids, or make it more or less sensitive to the ligands.