the nature of the binding between neurotransmitter and receptor site is binding constant.
nature of the binding between neurotransmitter and receptor site?
binding constant
if an endogenous ligand is found, the orphan receptor is "adopted" or "de-orphanized". an example is the nuclear receptor farnesoid x receptor (fxr) and the gpcr tgr5/gpcr19/g protein-coupled bile acid receptor, both of which are activated by bile acids. adopted orphan receptors in the nuclear receptor group include fxr, liver x receptor (lxr), and peroxisome proliferator-activated receptor (ppar). another example of an orphan receptor site is the pcp binding site in the nmda receptor, a type of ligand-gated ion channel. this site is where the recreational drug pcp works, but no endogenous ligand is known to bind to this site.
orphan receptor
catterall "et al." hypothesized that some polypeptide neurotoxins that modify voltage-gated channels function via a "voltage-sensor trapping" mechanism. the hypothesis states that neurotoxins similar to poneratoxin, such as alpha-scorpion toxins, act upon sodium channels via binding to the channels' receptor site 3, which normally affects the channels' ability to inactivate. therefore, receptor site 3 neurotoxins often affect sodium channels by slowing or blocking inactivation. normally, the region of the channel where neurotoxin receptor site 3 is undergoes a conformational change of an outward movement to lead to inactivation. receptor site 3 neurotoxins are proposed to prevent this conformational change via interaction with acidic and hydrophobic amino acid residues at that site.
poneratoxin