The Holin superfamily IV is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total.
The Holin superfamily IV includes the TC families:
Superfamily IV includes four TC families, which includes members from Firmicutes, Actinobacteria and Fusobacteria. Their average sizes are (in amino acyl residues (aas)):
TC# 1.E.10 - 138 ± 6 aas
TC# 1.E.16 - 149 ± 15 aas
TC# 1.E.19 - 141 ± 12 aas
TC# 1.E.40 - 173 ± 149 aas
Thus, there is very little size variation among family members, except for family 40, which has members larger than the other proteins in this superfamily. All members of families 10 and 19 and many members of family 16 appear to have 3 transmembrane segments (TMSs), but some members of this last family are predicted to have 4 TMSs. The extra TMS in these proteins is at their N-termini.