Cryo-EM structures of human TMEM120A and TMEM120B

TMEM120A (Transmembrane protein 120A) was recently identified as a mechanical pain sensing ion channel named as TACAN, while its homologue TMEM120B has no mechanosensing property1. Here, we report the cryo-EM structures of both human TMEM120A and TMEM120B. The two structures share the same dimeric assembly, mediated by extensive interactions through the transmembrane domain (TMD) and the N-terminal coiled coil domain (CCD). However, the nearly identical structures cannot provide clues for the difference in mechanosensing between TMEM120A and TMEM120B. Although TMEM120A could mediate conducting currents in a bilayer system, it does not mediate mechanical-induced currents in a heterologous expression system, suggesting TMEM120A is unlikely a mechanosensing channel. Instead, the TMDs of TMEM120A and TMEM120B resemble the structure of a fatty acid elongase, ELOVL7, indicating their potential role of an enzyme in lipid metabolism.