The small conductance mechanosensitive ion channel (MscS)-like (MSL) proteins in plants are evolutionarily conserved homologs of the bacterial small conductance mechanosensitive ion channels. As the sole member of the Arabidopsis MSL family localized in the mitochondrial inner membrane, MSL1 is essential to maintain the normal membrane potential of mitochondria. Here, we report a cryoelectron microscopy (cryo-EM) structure of Arabidopsis thaliana MSL1 (AtMSL1) at 3.3 Å. The overall architecture of AtMSL1 is similar to MscS. However, the transmembrane domain of AtMSL1 is larger. Structural differences are observed in both the transmembrane and the matrix domain of AtMSL1. The carboxyl-terminus of AtMSL1 is more flexible and the β-barrel structure observed in MscS is absent. The side portals in AtMSL1 are significantly smaller, and enlarging the size of the portal by mutagenesis can increase the channel conductance. Our study provides a framework for eukaryotic MscS-like mechanosensitive ion channels and the gating mechanism of the MscS family.

植物中的小电导机械敏感离子通道（MscS）样（MSL）蛋白是细菌小电导机械敏感离子通道的进化保守同源物。作为拟南芥MSL家族的唯一成员，它位于线粒体内膜，MSL1对于维持线粒体的正常膜电位至关重要。在这里，我们报告拟南芥的低温电子显微镜（cryo-EM）结构MSL1（AtMSL1）为3.3。AtMSL1的总体体系结构类似于MscS。但是，AtMSL1的跨膜域较大。在AtMSL1的跨膜和基质域中均观察到结构差异。AtMSL1的羧基末端更具柔韧性，并且缺少在MscS中观察到的β-桶结构。AtMSL1中的侧门明显较小，通过诱变扩大门的大小可以增加通道电导。我们的研究为真核MscS样机械敏感离子通道和MscS家族的门控机制提供了框架。