iGABASnFR1 is a genetically encoded fluorescent sensor designed for in vivo detection of GABA (γ-aminobutyric acid). iGABASnFR1 is a fusion protein composed of an N-terminal secretion signal, the GABA-binding Pf622 protein from Pseudomonas fluorescens, with insertion of a circularly permuted form of sfGFP after residue 276 of Pf622, a Tag:MYC tag and a C-terminal transmembrane domain from PDGFR (which anchors the protein to the membrane and displays it on the extracellular side). It also contains a number of additional mutations introduced during optimization of the sensor; these are optimized linkers (L1-LAQVR, L2-AN), two mutations in the Pf622 sequence (F101L - a hinge mutation, and N260A - an interface and expression mutation), and a mutation in the sfGFP sequence (F145W) (PMID:31308547).