The crystal structure of the CmABCB1 G132V mutant, which favors the outward-facing state, reveals the mechanism of the pivotal joint between TM1 and TM3

CmABCB1 is a homologue of human P-glycoprotein, which extrudes various substrates by iterative cycles of conformational changes between the inward- and outward-facing states. Comparison of the inward- and outward-facing structures of CmABCB1 suggested that pivotal joints in the transmembrane domain regulate the tilt of transmembrane helices. Transmembrane helix 1 (TM1) forms a tight helix-helix contact with TM3 at the TM1-3 joint. Mutation of Gly132 to valine at the TM1-3 joint, G132V, caused a 10-fold increase in ATPase activity, but the mechanism underlying this change remains unclear. Here, we report a crystal structure of the outward-facing state of the CmABCB1 G132V mutant at a 2.15 angstrom resolution. We observed structural displacements between the outward-facing states of G132V and the previous one at the region around the TM1-3 joint, and a significant expansion at the extracellular gate. We hypothesize that steric hindrance caused by the Val substitution shifted the conformational equilibrium toward the outward-facing state, favoring the dimeric state of the nucleotide-binding domains and thereby increasing the ATPase activity of the G132V mutant.

Automated summary

This study reported the crystal structure of the outward-facing state of the CmABCB1 G132V mutant, showing that the conformational change caused by the valine substitution led to an increase in ATPase activity, although the specific mechanism behind this remains unclear.