Ahmed M, Borsch C M, Neyfakh A A, Schuldiner S
Department of Medicinal Chemistry and Pharmacognosy (M/C 781), University of Illinois, Chicago.
J Biol Chem. 1993 May 25;268(15):11086-9.
The Bacillus subtilis multidrug transporter Bmr effluxes structurally diverse toxic compounds out of bacterial cells. Antihypertensive alkaloid reserpine reverses Bmr-mediated multidrug resistance by inhibiting drug transport. We have obtained a mutant of the bmr gene that provides a normal level of multidrug resistance, which can, however, only be reversed by very high concentrations of reserpine. Reduction of Bmr sensitivity to reserpine has been caused by the substitution of Leu for Val286 in the Bmr molecule. This mutation also led to a dramatic decrease of [3H]reserpine binding to membrane vesicles prepared from the Bmr-overexpressing bacteria. Leucine is larger than valine by one methylene group. Substitution of Val286 with a smaller residue, glycine, had an opposite effect. It led to increased sensitivity of Bmr to reserpine and increased affinity of reserpine binding to the membranes prepared from Bmr-overexpressing bacteria. Neither of the mutations significantly changed the sensitivity of Bmr to rescinnamine, a structural analog of reserpine. The results suggest that Val286 is involved in the formation of the reserpine-binding site of the Bmr molecule.
枯草芽孢杆菌多药转运蛋白Bmr可将结构多样的有毒化合物排出细菌细胞。抗高血压生物碱利血平通过抑制药物转运来逆转Bmr介导的多药耐药性。我们获得了一个bmr基因的突变体，其提供正常水平的多药耐药性，然而，只有在非常高浓度的利血平作用下才能被逆转。Bmr对利血平敏感性的降低是由于Bmr分子中第286位缬氨酸被亮氨酸取代所致。该突变还导致与过表达Bmr的细菌制备的膜囊泡结合的[3H]利血平显著减少。亮氨酸比缬氨酸多一个亚甲基。用较小的残基甘氨酸取代第286位缬氨酸则产生相反的效果。它导致Bmr对利血平的敏感性增加，以及利血平与过表达Bmr的细菌制备的膜的结合亲和力增加。这两种突变均未显著改变Bmr对利血平的结构类似物异利血平的敏感性。结果表明，第286位缬氨酸参与了Bmr分子利血平结合位点的形成。
