The diterpene forskolin has been demonstrated to affect proteins other than adenylyl cyclase. However, there has been relatively little information regarding the differences in the binding of forskolin at functionally diverse proteins. Analogs of forskolin have been developed which can be used to discriminate between adenylyl cyclase, the facilitated glucose transporter, and the P-glycoprotein multidrug transporter. The hydrogen binding requirements for forskolin interactions at the glucose transporter and the adenylyl cyclase have been determined and are very different. In addition, it has been shown that the affinity of forskolin for the Glut-4 glucose transporter is much higher than for the Glut-1 or Glut-3 transporter. However, the hydrogen bonding characteristics for forskolin binding to the Glut-1, Glut-3, and Glut-4 transporters are not very different. These data will be useful in developing a model for the forskolin binding site at the glucose transporter. Similar experiments are being carried out with adenylyl cyclase subtypes. In addition, experiments are being carried out to determine the structure activity relationships of forskolin for interactions with the P-glycoprotein multidrug transporter.
