Fig. 4.

Modification of adaptation sites reveals allosteric coupling throughout the HAMP-KCM. Methylation of the effector adaptation regions was mimicked by glutamine substitution. (A) Increased modification and decreasing charge in H1-2-Tar (QQQQ) shift the distribution at the adaptation region toward smaller distances, whereas decreased modification (EEEE) and increasing charge in H1-Tar shift the distribution to longer distances and amplify the peak centered around ∼50 Å. (B) Increased modification of H1-2-Tar decreases the distance distribution [P(r)] breadth and stabilizes the PIR, whereas in H1-Tar, decreased modification increases the P(r) breadth and destabilizes the PIR. (C) Modification at the adaptation region has no effect on PDS distributions in the hinge region for either effector. (D) Increased modification of H1-2-Tar has little effect on spin distributions in AS2 of the HAMP domain; however, decreased modification stabilizes the HAMP domain of H1-Tar toward the sharp bimodal distribution as seen in H1-2-Tar.