Electrical Fingerprinting Reveals Agonist Binding Sites Required for Activation of Homo-pentameric Cys-loop Receptors

BOUZAT C; RAYES D; DE ROSA MJ; SINE S

Boston, USA

Congreso; Biophysical Society 53rd Annual Meeting.; 2009

Biophysical Society

Ancestral neurotransmitter Cys-loop receptors were homo-pentamer harboring five identical agonist binding sites but most present day receptors are hetero-pentamers with only two binding sites. To understand why Cys-loop receptors evolved to utilize fewer than five binding sites, we disabled different numbers of sites and develop a method to monitor lifetimes of individual active receptors and the corresponding number of functional binding sites. We find that maximal open-channel lifetime is achieved when the neurotransmitter occupies three non-consecutive binding sites. Occupancy of one site allows receptor activation, although the open state is unstable; occupancy of two non-consecutive sites produces a much longer-lived open state appropriate for efficient activation. However, occupancy of a third site further increases channel lifetime, thus providing optimal stabilization of the active state. Maximal activation of homomeric receptors by agonist occupancy of less than the five potential sites enhances the rate of channel opening and increases agonist sensitivity. The results reveal that allosteric requirements dictated the number and location of the agonist binding sites, and provide an indispensable framework for further progress in drug design.