In: Biology
Briefly describe two key differences that contrast signaling between receptor tyrosine kinases (RTKs) and G-protein coupled receptors (GPCRs).
Ans- Receptor tyrosine kinase belongs to class of plasma membrane receptor having enzyme activity. The part of receptor protein extending into cytoplasm functions as tyrosine kinase, an enzyme which catalyse transfer of phosphate group from ATP to tyrosine. One receptor tyrosine kinase may activate ten or more different transduction pathways and cellular responses. Often more than one signal transduction pathway can be triggered once helping cell regulate and co-ordinate many aspects of cell growth and cell reproduction.
While G protein coupled receptor is a transmembrane protein taht works with the help of G protein, a protein that binds energy rich molecule GTP. It USA n example of epinephrine receptor. The activated G protein dissociates from receptor, diffuses along the membrane and then binds to the enzyme, altering it's shape and activity. Once activated it can trigger next step leading to cellular response. Binding of signalling molecule is reversible where like many ligand they bind and dissociate many times.
(i). In RTK first messenger is one of several growth hormones or insulin while in GPCR it is extracellular impermeable hydrophilic ligand molecules.
(ii). In RTk receptor structure is single pass membrane protein while in GPCR 7- pass transmembrane proteins
(iii). In RTK transducer is cytosolic phosphorylated domains with SH2 domains while in GPCR is G protein.
(iv). In RTK effector is GRBP2, PLC gamma etc, while in GPCR adenyly cyclase.
(v). Secondary messenger in RTK effector is inositol triphosphate, diacylgylecerol ,etc while in GPCR it is cyclic AMP.
(vi). Target cell response :
RTK - growth, alteration in gene expression, calcium outflux , division and development, alteration in gene expression, expression of AP1.
GPCR- modification of other enzymes, essential metabolic processes alterations, altered gene expression, PKA production, PLC production.