Related Research Articles
Holins are a diverse group of small proteins produced by dsDNA bacteriophages in order to trigger and control the degradation of the host's cell wall at the end of the lytic cycle. Holins form pores in the host's cell membrane, allowing lysins to reach and degrade peptidoglycan, a component of bacterial cell walls. Holins have been shown to regulate the timing of lysis with great precision. Over 50 unrelated gene families encode holins, making them the most diverse group of proteins with common function. Together with lysins, holins are being studied for their potential use as antibacterial agents.
The Holin superfamily II is a superfamily of putative pore-forming 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. The Holin superfamily II includes the TC families:
The Holin Superfamily III 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.
The putative actinobacterial holin-X (Hol-X) family was retrieved as a distant member of TC family 1.E.20, suggesting membership of the holin superfamily III. Most Hol-X proteins are less than 200 amino acyl residues (aas) in length and possess two transmembrane segments (TMSs). A representative list of proteins belonging to this family can be found in the Transporter Classification Database.
The Deinococcus/Thermus Holin (D/T-Hol) Family consists of a single protein with no close homologues ; however, its distant homology to members of the Holin superfamily III suggest an evolutionary relationship. The putative holin of Meiothermus silvanus is 108 amino acyl residues in length and possesses 3 transmembrane segments.
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 VI 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.
The Holin superfamily VII 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.
The Listeria Phage A118 Holin (Hol118) Family is a group of transporters belonging to the Holin Superfamily V. A representative list of proteins belonging to the Hol118 family can be found in the Transporter Classification Database.
The Holin Hol44 (Hol44) Family is a group of transporters belonging to the Holin Superfamily V. A representative list of proteins belonging to the Hol44 family from caudovirales and firmicutes can be found in the Transporter Classification Database.
The holin LLH family is a group of transporters belonging to the Holin superfamily VI. The Holin LLH family is found in Firmicutes and phage of Firmicutes as well as other bacteria. Members are fairly large, between 100 and 160 amino acyl residues in length, and have an N-terminal transmembrane segment (TMS). Some proteins, such as putative holin of Fusobacterium varium, may exhibit 2 TMSs. A representative list of proteins belonging to the Holin LLH family can be found in the Transporter Classification Database.
The Putative 3-4 TMS Transglycosylase-associated Holin Family is believed to be a group of holins that does not belong to one of the seven holin superfamilies. Homologues include thousands of diverse phage and bacterial proteins between 80 and 140 amino acyl residues (aas) in length that exhibit 3 to 4 transmembrane segments (TMSs). These proteins are holin-like in their size and topology and are designated 'Transglycosylase-associated', 'Putative holin', 'Phage-like transmembrane protein', 'YeaQ protein', etc. in the NCBI protein database. As of early 2016, they remain functionally uncharacterized. They derive from a wide range of bacterial and archaeal phyla including both Gram-negative and Gram-positive bacteria. These proteins are related to the RDD family in the conserved domain database. A representative list of proteins belonging to the T-A Hol family can be found in the Transporter Classification Database.
The CaulobacterPhage Holin (CauHol) Family consists of several putative holins of 157 to 159 amino acyl residues (aas) in length that exhibit 2 transmembrane segments (TMSs). They derive from phage specific for Caulobacter species. These proteins are not functionally characterized. A representative list of proteins belonging to the CauHol family can be found in the Transporter Classification Database.
The β-proteobacterial holin (BP-Hol) family is a small family that includes members derived from a number of Burkholderia phage as well as a Poloromonas species. As of April 3, 2016, this family belongs to the Holin superfamily II. Members of Saier Bioinformatics Lab at University of California, San Diego found that the BP-Hol family is most closely related to the T7 holin family. These proteins are of 60 to 110 amino acyl residues (aas) in length and exhibit 1 or 2 transmembrane segments (TMSs). Some are annotated as type II hollins and may be related to members of the T7 Holin family, although BP-Hol proteins remain functionally uncharacterized. A representative list of the proteins belonging to the BP-Hol family can be found in the Transporter Classification Database.
The Putative Listeria Phage Holin (LP-Hol) Family consists of several small proteins of 41 amino acyl residues (aas) and 1 transmembrane segment (TMS). They can be found in several Listeria phage as well as in Listeria monocytogenes. While annotated as holins, these proteins remain functionally uncharacterized. A representative list of proteins belonging to the LP-Hol family can be found in the Transporter Classification Database.
The Flp/Fap Pilin Putative Holin (FFPP-Hol) Family is a large diverse family with members from many bacterial phyla. Some members are annotated as Flp or Fap pilin subunits; others are identified as Holin BlyA family members. They range in size of 50 to 80 amino acyl residues (aas) with a single N-terminal transmembrane segment (TMS) although one member has 99 aas and 2 TMSs. Flp homologues are included in TCDB under TC# 3.A.7.13.1 (pXO1-63) and TC# 3.A.7.15.1 (Flp-1). As on March 2016, their precise functions appear to be unknown. A representative list of proteins belonging to the FFPP-Hol family can be found in the Transporter Classification Database.
The Brachyspira holin (B-Hol) Family consists of several proteins from the GTA holin of Brachyspira hyodysenteriae, which facilitates gene transfer agent-release to VSH-1 holin of Brachyspira pilosicoli. VSH-1 is thought to participate in cell lysis. These proteins range in size from about 85 to 145 amino acyl residues (aas) and exhibit between 2 and 4 transmembrane segments (TMSs). A representative list of proteins belonging to the B-Hol family can be found in the Transporter Classification Database.
The Putative 3 TMS Holin (3-Hol) Family is large, consisting of many members derived from proteobacteria and their phage, all of small size and usually with 3 transmembrane segments (TMSs). A representative list of the proteins belonging to this family can be found in the Transporter Classification Database. While many of the proteins belonging to this family are annotated in holins, they remain functionally uncharacterized.
The Prophage Hp1 Hol (Hp1Hol) Family consists of a single putative holin of 69 amino acyl residues in length, exhibiting what appears to be a single transmembrane segment (TMS). It is derived from the firmicute, Clostridium hathewayi DSM 13479. This protein is functionally uncharacterized and does not appear to be homologous to other holins. It does, however, show 31% identity to a heavy metal transporter from Dethiosulfovibrio peptidovorans.
The Putative Bacterial Archaeal Holin(BAH) Family consists of several uncharacterized proteins. However, these proteins were retrieved when functionally characterized holins from the T-A Hol family were BLASTED against the NCBI database, and thus may be related to the T-A Hol family. Most BAH proteins are between 125 and 140 amino acyl residues (aas) in length and exhibit 4 transmembrane segments (TMSs), although at least one putative holin is almost 260 aas long. A representative list of proteins belonging to the BAH family can be found in the Transporter Classification Database.
References
- ↑ "Holin Superfamily V". Transporter Classification Database. Retrieved 2016-03-20.
- ↑ Reddy, Bhaskara L.; Saier Jr., Milton H. (2013-11-01). "Topological and phylogenetic analyses of bacterial holin families and superfamilies". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1828 (11): 2654–2671. doi:10.1016/j.bbamem.2013.07.004. PMC 3788059 . PMID 23856191.
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