The Holin Superfamily I (aka the CDD phage holin1 superfamily) is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members.
Its main constituent is the Phi11 Holin (φ11 Holin) Family.[1] This family is made up of over 270 putative pore-forming proteins, all from Bacillota. On average, proteins belonging to the holin I superfamily are about 100 amino acyl residues (aas) in length, although a large size variation exists among proteins of this superfamily. There does not seem to be deviation from the standard two transmembrane segments that these proteins possess.[2] [3]