 It is important to note that the M1 and M2 helices of the same subunit are not connected; instead, the M1 helix of one subunit makes tight contact with the M2 helix of the adjacent subunit.With additional interactions through a salt bridge in Ec-MscL, the entire complex is secured together.The N-terminal S1 domains of Tb-MscL were not resolved in the crystal structure, only inferred as short α helices bundled together to form an additional cytoplasmic gate; however, subsequent cysteine cross-linking experiments supported this proposed configuration.