THE BIOCHEMICAL EFFECT OF THE NATURALLY-OCCURRING TRP64-]ARG MUTATIONON HUMAN BETA-3-ADRENOCEPTOR ACTIVITY

A Trp-->Arg mutation at amino acid position 64 in the human beta 3-adr enoceptor is reportedly associated with morbid obesity: carriers suffe r from increased gain in mass, early-onset diabetes, insulin resistanc e. and an increased waist-to-hip ratio [Clement. K., Vaisse. C., Manni ng, B. S., Basdevant, A., Guy-Grand, B., Ruiz, J., Silver. K. D., Shul diner, A. R., Froguel. P. & Strosberg, A. D. (1995) N. Engl. J. Med. 3 33, 352-354]. Here, we report the stable expression of the genes encod ing the wild-type or the [Arg64]beta 3-adrenoceptor in two different c ell types: hamster CHO-K1 and human HEK293. Tile mutated receptor disp layed unchanged pharmacological values compared to the wild type for t he binding inhibition (K-i) and adenylyl cyclase activation constants (K-act) in two independent clones of both cell lines, However. maximal cAMP accumulation was significantly reduced in response to various be ta 3-adrenergic agonists, including endogenous catecholamines, (-)-epi nephrine and (-)-norepinephrine, the non-selective agonist (-)-isoprot erenol, and the beta 3-adrenergic selective agonist CGP 12177A. Treatm ent with Pertussis toxin did not restore the adenylyl cyclase activity to that of the wild type, suggesting that the reduction in cAMP accum ulation observed in cells expressing [Arg64]beta 3-adrenoceptor is nut due to enhanced interaction of the beta 3-adrenoceptor with the inhib itory G(i) protein.