In bacteria,such as E.coli, chemotaxis – movementtoward or away from chemical is achieved by rotation of propeller-likestructure called flagella.
Bacteria senses chemical gradients by virtue oftheir transmembrane chemoreceptors, known as methyl-accepting chemotaxisproteins (MCP). These MCPs screen and record the cell’s recent chemical historyin the form of reversible methylation of specific amino acid residues in theircytoplasmic signaling domain. When the current ligand bound state fails tocoincide with the methylation record, the MCP initiates a motor controlresponse using a common set of six cytoplasmic signaling Che proteins thatregulate flagellar rotation. The signaling protein CheW and CheA generatereceptor signals from MCPs through phosphorylation mechanism. The CheY and CheZprotein control motor responses. The phosphorylated form of CheY relays and initiatesmotors response by binding to the flagellar motor FliM protein causingclock-wise (CW) rotation of flagella that results into cell tumbling/ turning movement.
The CheZ protein controls the dephosphorylation rate of phospho-CheY. Theenzyme CheR and CheB regulate methylation state of MCP. Under isotropicchemical environments, bacteria swims in a random walk pattern generated byalternating episodes of counter-clockwise (CCW) and clockwise (CW) flagellarrotation. In an attractant or repellent gradient, the bacteria chemotax and directtheir overall motion (towards or away) based on the gradient by modulating thefrequency of the next tumbling (CW) event.
Thus, for optogenetic regulation, wetargeted CheY protein that regulates the clock wise (CW) or tumbling movementin bacteria using optogenetic protein LOV2 (light, oxygen and voltage 2)derived from Avena sativa Phototropin1. LOV2 domainconsists of a light absorbing flavin mononucleotide-binding core domain and C-terminal? helical region called the J?-helix. Upon irradiation with blue light J? helixundergoes large conformation change.This light-induced conformational changes inLOV2 domain will thus, perturbed and disorder native structure of linked CheYprotein making it inactive, which in turn results into chemotaxis inhibition.