TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
1.E.19.1.1









Holin (161 aas)

Bacteria
Actinobacteria
Holin of Mobiluncus mulieris
1.E.19.1.2









Uncharacterized protein

Bacteria
Firmicutes
Uncharacterized protein of Lachnospiraceae bacterium
1.E.19.1.3









Putative holin of 152 aas and 3 TMSs

Bacteria
Firmicutes
Putative holin of Brevibacillus brevis
1.E.19.1.4









Uncharacterized protein

Viruses
Caudovirales
Uncharacterized protein of Bacillus phage IEBH
1.E.19.1.5









Uncharacterized protein (142 aas)

Bacteria
Firmicutes
Uncharacterized protein of Clostridium bolteae
1.E.19.1.6









Holin

Bacteria
Actinobacteria
Holin of Corynebacterium diphtheriae
1.E.19.1.7









Putative holin of 139 aas nd 3 TMSs

Bacteria
Thermotogae
Putative holin of Petrotoga mobilis
1.E.19.1.8









Prophage lambda Sa04 protein

Bacteria
Firmicutes
Sa04 protein of Megasphaera elsdenii
1.E.19.1.9









Holin (129 aas)

Bacteria
Fusobacteria
Fusobacterium sp. ZP-0
1.E.19.1.10









Phage-related holin of 142 aas and 4 TMSs

Bacteria
Tenericutes
Holin of Acholeplasma laidlawii
1.E.19.1.11









Holin of 141 aas and 2 TMSs

Bacteria
Chloroflexi
Holin of Dehalococcoides ethenogenes
1.E.19.1.12









Holin of 137 aas and 2 TMSs (Jin et al. 2013).

Viruses
Caudovirales
Holin of Geobacillus phage GBSV1
1.E.19.1.13









Toxin secretion/holin system; holin of 124 aas

Bacteria
Tenericutes
Holin of Mycoplasma sp.
1.E.19.1.14









Putative holin of 142 aas

Bacteria
Chloroflexi
Putative holin of Herpetosiphon aurantiacus
1.E.19.1.15









Putative holin of 141 aas and 3 TMSs

Bacteria
Bacteroidetes/Chlorobi group
Putative holin of Alistipes shahii
1.E.19.1.16









Holin of 138 aas and 3 TMSs (Kong and Ryu 2015).

Viruses
Caudovirales
Holin of Bacillus phage PBC1
1.E.19.1.17









Holin of 139 aas and 2 TMSs.

Bacteria
Bacteroidetes
Holin of Bacteroides fragilis
1.E.19.2.1









Holin of 170 aas and 3 TMSs

Bacteria
Firmicutes
Holin of Macrococcus caseolyticus
1.E.19.2.2









Staphylococcus aureus phage P68 holin, hol15 (Takác et al. 2005).

Viruses
Caudovirales
Hol15 of Staphylococcal phage P68
1.E.19.2.3









phage-like holin, YqxH1 (135 aas)

Bacteria
Firmicutes
YqxH1 of Bacillus amyloliquefaciens
1.E.19.3.1









The C. difficile holin, TcdE.  TcdE acts as a holin-like protein to facilitate the release of C. difficile toxins A and B to the extracellular environment, but, unlike most phage holins, it does not cause the non-specific release of cytosolic contents. TcdE is thus a bacterial holin that releases toxins into the environment by a phage-like system (Tan et al. 2001; Govind and Dupuy 2012).  Different isoforms have differing activities in toxin release (Govind et al. 2015). An autolysin, Cwp19 (L7PGA3), may also play a role in toxin release (El Meouche and Peltier 2018). Adaptation of this phage-derived holin/endolysin system to toxin transport has been discussed (Mehner-Breitfeld et al. 2018). Thus, TcdE exists as three isoforms, differing with respect to their N-terminal extensions.  The longest TcdE isoform has a moderate effect on cell growth, whereas the shortest isoform strongly induces lysis. The effect of the longest isoform was inhibitory for cell lysis, implying a regulatory function of the N-terminal 24 residues.  Mehner-Breitfeld et al. 2018 analyzed the PaLoc sequence of 44 C. difficile isolates and found that four of these encode only the short TcdE isoform, and the most closely related holins from C. difficile phages only possess one of these initiation codons, indicating that the N-terminal extensions of TcdE evolved in C. difficile.

Bacteria
Firmicutes
TcdE of Clostridium difficile
1.E.19.3.2









Holin of 141 aas and 3 TMSs, TcsE (Sirigi Reddy et al. 2013).

Bacteria
Firmicutes
TcsE of Clostridium sordellii
1.E.19.4.1









Holin of Clostridium phage phi3626.  The function has been demonstrated (Zimmer et al. 2002).  The charge distribution of this 2 TMS protein suggestions that the β-turn between TMSs 1 and 2, with 7 lys and arg residues, is in the cytoplasm and the N- and C-termini are in the periplasm (Zimmer et al. 2002).

Viruses
Caudovirales
Holin of Clostridium phage phi3626
1.E.19.4.2









Toxin secretion holin of 137 aas and 3 TMSs.

Bacteria
Actinobacteria
Holin of Atopobium minutum
1.E.19.4.3









Putative holin of 158 aas and 3 TMSs.

Bacteria
Actinobacteria
Putative holin of Gardnerella vaginalis
1.E.19.5.1









Holin of 162 aas and 3 TMSs

Bacteria
Proteobacteria
Putative holin of Desulfovibrio vulgaris
1.E.19.6.1









Putative holin of 178 aas and 4 TMSs

Bacteria
Bacteroidetes/Chlorobi group
Holin of Pedobacter saltans
1.E.19.6.2









Putative holin of 181 aas and 3 TMSs

Bacteria
Bacteroidetes/Chlorobi group
Holin of Capnocytophaga sputigena
1.E.19.6.3









Putative holin of 170 aas and 3 TMSs

Bacteria
Bacteroidetes/Chlorobi group
Holin of Cyclobacterium marinum (Flectobacillus marinus)