Following theiractivation upon binding to ligand, G protein–coupledreceptors, GP
ID: 3455 • Letter: F
Question
Following theiractivation upon binding to ligand, G protein–coupledreceptors, GPCRs,
in turn activate Gproteins and thereby initiate a signaling cascade. Followingligand
binding, GPCRsbecome phosphorylated by G protein receptor kinases (GRKs) which,in
turn, leads todesensitization of the receptor such that continued stimulation byligand
results in a waningresponsiveness of the cell. Arrestins are proteins that bind toGPCRs
and are involved inthis desensitization. In order to understandGPCR-arrestin
interactions,the 122adrenergic receptor (122AR), a GPCR, and its interaction with
arrestin aresubjected to study.
a. A cell line expressing the 122AR is incubated in epinephrine, a ligand forthis
receptor, for 5minutes. The cells are then lysed and the 122AR is
immunoprecipitatedfrom the lysate. To determine if arrestin is bound to the
receptor, theimmunoprecipitate is examined by Western blotting using anantibody
directedagainst arrestin. The experiment isrepeated, but this time prior to and
during epinephrineaddition the cells are incubated in an inhibitor that blocks2-AR
phosphorylation bythe kinase GRK2 (BARK). The data are shown below. How
does the activationstate of the receptor affect arrestin binding? What information
Following theiractivation upon binding to ligand, G protein?coupledreceptors, GPCRs, in turn activate Gproteins and thereby initiate a signaling cascade. Followingligand binding, GPCRsbecome phosphorylated by G protein receptor kinases (GRKs) which,in turn, leads todesensitization of the receptor such that continued stimulation byligand results in a waningresponsiveness of the cell. Arrestins are proteins that bind toGPCRs and are involved inthis desensitization. In order to understandGPCR-arrestin interactions,the beta12beta2adrenergic receptor (beta12beta2AR), a GPCR, and its interaction with arrestin aresubjected to study. a. A cell line expressing the beta12beta2AR is incubated in epinephrine, a ligand forthis receptor, for 5minutes. The cells are then lysed and the beta12beta2AR is immunoprecipitatedfrom the lysate. To determine if beta arrestin is bound to the receptor, theimmunoprecipitate is examined by Western blotting using anantibody directedagainst beta arrestin. The experiment isrepeated, but this time prior to and during epinephrineaddition the cells are incubated in an inhibitor that blocksbeta2-AR phosphorylation bythe kinase GRK2 (BARK). The data are shown below. How does the activationstate of the receptor affect beta arrestin binding? What information do the kinase inhibitor studiesprovide about beta arrestin binding to thereceptor? - inhibitor + inhibitor min in epinephrine: 0 5 0 5Explanation / Answer
Hmm....fairly interesting question and I can't ensure if my answerwill be necessarily entirely correct so you'll have to double checkit with a friend/professor/journal article. Are we to incorporatethe data somehow in our answers? I can only give you textbook typeof answers. Q1: How does the activation state of thereceptor affect arrestin binding? A1: arrestin,an inhibitor protein, binding is facilitated(andto an extent, accelerated) by the inactivation of -adrenergicreceptors by means of stimulation by receptor agonists. Theinactivation of -adrenergic receptors is by the-adrenergic receptor kinase (BARK ) phosphorylating. BARKactivation relies on a translocation of the enzyme to themembrane. So I suppose you would be able to pull your answer from there(you've got to understand the process/relations and then think forabit). What would activating the receptor do rather than when it'sinactivated? Q2: What information do the kinase inhibitor studies provide about arrestin binding to the receptor? -arrestin binding to the receptor( -adrenergicreceptor) is facilitated by the phosphorylation of BARK whichinactivates the -adrenergic receptors(receptor agonistsstimulate it) Good luck.