Fig. 3: Both GB1 and GB2 subunits are required for GABAB receptor activation by mechanical forces.
From: GABA-independent activation of GABAB receptor by mechanical forces
a–c Left: IP1 production in HEK293 cells transfected with the indicated constructs, along with Gqi9 under either suspension or adhesion conditions: (a): vector, GABAB receptor (GB1 and GB2), GB1 only or GB2 only; (b): vector, GABAB receptor, GABAB-ΔG (mutant with L685 in GB2 substituted with Phenylalanine that fails to couple G protein), or GABAB-ΔB (mutant with the residues S276 and E465 in GB1 mutated to Analine that fails to bind GABA); (c): vector or GABAB receptor, treated with or without antagonist CGP54626 (50 μM, 30 min). Data are present as mean ± s.e.m. from at least three biologically independent experiments (from left to right, a, n = 4, 4, 4, 4; b, n = 6, 6, 4, 4; c, n = 5, 3, 6, 4) each performed in triplicates, and analyzed using unpaired t test (two-tailed) to determine significance. ***p < 0.001, *p < 0.05, not significant (ns) > 0.05. Right: Model of the traction force-induced GABAB receptor activation through the closure of GB1VFT-induced LB2GB1 and LB2GB2 in contact. The traction force-activated GABAB receptor requires both GB1 and GB2, and relies on GB2 for G protein coupling. Whereas the traction force-activated GABAB receptor is independent of GABA binding, preventing VFTGB1 closure by GABAB receptor antagonist CGP54626, abolishes traction force-induced GABAB receptor activation, indicating that the closure of GB1VFT-induced LB2GB1 and LB2GB2 in contact is important for traction force-induced GABAB receptor activation.
