Question: how many gpcrs are there?
Answer: Estimates of the number of GPCRs in the human genome vary widely. Based on their sequences, as well as on their known or suspected functions, there are estimated to be five or six major classes of GPCR. In a recent analysis of the GPCRs in the human genome, more than 800 GPCRs were listed (Fredriksson et al., 2003).