If you are sure that no sequence rearrangements exist in the cloned gene, then you should avoid potential association of angiotensin II receptor type 1 with the E. coli outer membrane protein A, as follows from a reference below. Some heterologous proteins affect functions of a bacterial host and can't be overexpressed. If  the protein is detectable, then you can purify it without overexpression to get enough protein for many assays. Otherwise, try lower temperature incubation at 28-30°C, it might improve the solubility of AGTR1. Other strategies are based on using low expression vectors, preventing undesired protein functions, cloning in eucaryote cells, etc. 

http://jid.oxfordjournals.org/content/209/3/409.long

Dear Wisdom,

In addition to the excellent advices of Vehary, I would suggest to pick more than one colony to perform the induction (often, each colonies have very different overexpression levels). Also, you can do curves of time, from 1 to 18 hs/temperature, 25-28-30-37°C/ and inductor concentration, in order to optimize your overexpression conditions.

Thank you very much dear Vehary Sakanyan and Cristián Quintero, your contributions are very helpful @Vehary Sakanyan: many thanks for the literature @Cristián Quintero i have 8 colonies and earlier sequenced them all. the sequencing result showed that the gene had successfully been cloned in pGEX. I attempt growing under different temperature.

Dear Wisdom,

I've noticed that my suggestion and that of Cristian have been useful for you. Please, could you press green symbol for the appreciation of our contributions. Thanks