1.E.2.1.1
Lysis protein S of phage lambda, holin S105.  The lambda-holin protein can mediate a caspase-independent non-apoptotic mode of cell death (Agu et al. 2007).  Topological class I with three TMSs.  The N-terminus is outside and the C-terminus is inside (Graschopf and Bläsi 1999; Gründling et al. 2000).  Nearly identical to the holin of Shigella phage Sf6 (Dover et al. 2016).  It lambda protein has a three-helix topology with an unstructured C-terminal domain, as well as at least one interface on TMS1 which is exposed to the lumen of the hole, and a highly constrained steric environment suggestive of a tight helical packing interface at TMS2 (Morris et al. 2023).