Figure 2.

Effect of Orco CBS mutation on the odor response in solely Or22a/Orco expressing OSNs. (a) Scheme of a Drosophila melanogaster antenna. The third segment is covered with sensilla that house the dendrites of up to four OSNs. OSNs that express ORs (odorant receptor) are present in basiconic and trichoid sensilla and coeloconic sensilla house IR expressing OSNs. (b) Schematic view of insect ORs formed by heptahelical Or22a and Orco (co-receptor) proteins. The second intracellular loop of Orco contains the highly conserved CaM binding site ³³⁶SAIKYWVER³⁴⁴. (c) GCaMP labelled fluorescence intensity of Or22a/Orco OSNs. (d) Time course of Ca²⁺ fluorescence responses obtained OrcoWT OSNs and OrcoK339N OSNs upon OR stimulation with 100 µM ethyl hexanoate (n = 11 for OrcoWT, n = 11 for OrcoK339N). (e) Concentration response relationship for OrcoWT and OrcoK339N (8 ≤ n ≤ 10). Curves represent sigmoidal fits described by Hill coefficient 0.777 (OrcoWT), 0.9525 (OrcoK339N), and EC₅₀ of 13 µM (OrcoWT), 42 µM (OrcoK339N). (f) Maximum fluorescence response (Max ∆F/F₀ (%)) obtained by subtracting the base level at 50 s from the maximum Ca²⁺ fluorescence at 1 mM ethyl hexanoate. n = number of antennae. Two-tailed unpaired t- test, **P < 0.01. Data given as mean ± SEM. Scale bar of antenna: 20 µm.