Fig. 5.

Model for triggering of lysis with SAR endolysins. (A) A SAR endolysin is initially tethered in an inactive form to the energized membrane, in which the holin protein accumulates without affecting the pmf. (B) At the programmed lysis time, the holin triggers, disrupting the membrane sufficiently to abolish the pmf, and perhaps also to assist the liberation of the endolysin from the membrane, which results in activation of the endolysin. In contrast, with the canonical lysozymes of T4, λ, and T7, the endolysin accumulates in its active form in the cytosol (C) and, when the holin triggers, is released to the cell wall by membrane disruption sufficient to allow passage of large proteins (D).