Related Research Articles
Lysins, also known as endolysins or murein hydrolases, are hydrolytic enzymes produced by bacteriophages in order to cleave the host's cell wall during the final stage of the lytic cycle. Lysins are highly evolved enzymes that are able to target one of the five bonds in peptidoglycan (murein), the main component of bacterial cell walls, which allows the release of progeny virions from the lysed cell. Cell-wall-containing Archaea are also lysed by specialized pseudomurein-cleaving lysins, while most archaeal viruses employ alternative mechanisms. Similarly, not all bacteriophages synthesize lysins: some small single-stranded DNA and RNA phages produce membrane proteins that activate the host's autolytic mechanisms such as autolysins.
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 Phi11 Holin Family constitutes the Holin Superfamily I.
The Phage 21 S Family is a member of the Holin Superfamily II.
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 T4 Holin Family is a group of putative pore-forming proteins that does not belong to one of the seven holin superfamilies. T-even phage such as T4 use a holin-endolysin system for host cell lysis. Although the endolysin of phage T4 encoded by the e gene was identified in 1961, the holin was not characterized until 2001. A representative list of proteins belonging to the T4 holin family can be found in the Transporter Classification Database.
The Lactococcus lactis Phage r1t Holin Family is a family of putative pore-forming proteins that typically range in size between about 65 and 95 amino acyl residues (aas) in length, although a few r1t holins have been found to be significantly larger. Phage r1t holins exhibit between 2 and 4 transmembrane segments (TMSs), with the 4 TMS proteins resulting from an intragenic duplication of a 2 TMS region. A representative list of the proteins belonging to the r1t holin family can be found in the Transporter Classification Database.
The Neisserial Phage-associated Holin (NP-Holin) Family is a family of small proteins, between 47–53 amino acyl residues in length, that exhibit a single N-terminal transmembrane segment (TMS). Although annotated as phage proteins or holins, NP-Holin proteins are not yet functionally characterized, thus more research is needed to confirm holin activity. A representative list of proteins belonging to the NP-Holin family can be found in the Transporter Classification Database.
The SPP1 Holin Family consists of proteins of between 90 and 160 amino acyl residues (aas) in length that exhibit two transmembrane segments (TMSs). SPP1 is a double-stranded DNA phage that infects the Gram-positive bacteria. Although annotated as holins, members of the SPP1 family are not yet functionally characterized. A representative list of proteins belonging to the SPP1 Holin family can be found in Transporter Classification Database.
The Actinobacterial 1 TMS Holin Family consists of proteins found in actinobacteria, their conjugative plasmids and their phage. They are usually between 90 and 140 amino acyl residues (aas) in length and exhibit 1 or sometimes even 2 transmembrane segments despite the families name. Although some are annotated as phage proteins or holins, members of the A-1 family are not yet functionally characterized. A representative list of proteins belonging to the A-1 Holin family can be found in the Transporter Classification Database (TCDB).
The Mycobacterial 1 TMS Phage Holin Family was identified and recognized by Catalao et al. (2012). Members of this family are found in mycobacterial phage, exhibit a single transmembrane segment (TMSs), and are about 75 to 95 amino acyl residues in length. Although annotated as holins, members of this family are not yet functionally characterized. A representative list of proteins belonging to this family can be found in the Transporter Classification Database.
The Phage T1 Holin Family is represented in enterobacterial phages T1, RTP and F20, Klebsiella phage KP36, and Escherichia phage ADB-2. All of these possess a putative holin that share a high level of identity. Additionally, Gp9 of E. coli phage phiE49 is similar in sequence. These proteins are short, 55 to 71 amino acyl residues (aas) in length, and exhibit a single transmembrane segment (TMS). A representative list of proteins belonging to the T1 Holin family can be found in the Transporter Classification Database.
The Staphylococcusphage P68 Putative Holin Family consists of a single putative holin from Staphylococcus aureus phage P68 that is 92 amino acyl residues (aas) in length and exhibits 2 transmembrane segments (TMSs). While annotated as a holin, this protein has not been functionally characterized.[2]
The Putative Lactococcus lactis Holin (LLHol) Family consists of just a few proteins from Lactococcus lactis species and their phage. These proteins are small, between 61 and 78 amino acyl residues (aas) in length, and exhibit one or two transmembrane segments (TMSs). As of March 2016, LLHol proteins remain functionally uncharacterized. They are not demonstrably homologous to members of other holin families and thus do not belong to one of the seven holin superfamilies. A representative list of proteins belonging to the LLHol 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 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 Actinobacterial Phage Holin (APH) Family is a fairly large family of proteins between 105 and 180 amino acyl residues in length, typically exhibiting a single transmembrane segment (TMS) near the N-terminus. A representative list of proteins belonging to the APH family can be found in the Transporter Classification Database.
The Enterobacterial Holin (EBHol) Family consists of many closely related proteins of 100 to 120 amino acyl residues (aas) in length with a single C-terminal transmembrane segment (TMS). They derive from γ-proteobacteria of many genera: Salmonella, Escherichia, Klebsiella and Photorhabdus, and their phage. As of March 2016, these proteins have not been functionally characterized. A representative list of proteins belonging to the EBHol family can be found in the Transporter Classififcation Database.
The Firmicute PhageφU53 Holin Family consists of putative holins that range in size from 117 to 124 amino acyl residues (aas) in length and exhibit 3 transmembrane segments (TMSs) found in Bacillota phage. While annotated as holins, it appears as though many members of the φU53 holin family are not yet functionally characterized. A representative list of homologues can be found in the Transporter Classification Database.
The ArpQ Holin Family consists of a single holin-like protein 58 amino acyl residues (aas) in length with 2 transmembrane segments (TMSs). This protein is encoded by the arpQ gene in Enterococcus hirae. While annotated as a holin, it is not functionally characterized.
References
- ↑ Labrie, Steve; Vukov, Natasa; Loessner, Martin J.; Moineau, Sylvain (2004-04-01). "Distribution and composition of the lysis cassette of Lactococcus lactis phages and functional analysis of bacteriophage ul36 holin". FEMS Microbiology Letters. 233 (1): 37–43. doi: 10.1016/j.femsle.2004.01.038 . hdl: 20.500.11850/51071 . ISSN 0378-1097. PMID 15043867.
- 1 2 Paulsen, I. T.; Banerjei, L.; Myers, G. S. A.; Nelson, K. E.; Seshadri, R.; Read, T. D.; Fouts, D. E.; Eisen, J. A.; Gill, S. R. (2003-03-28). "Role of mobile DNA in the evolution of vancomycin-resistant Enterococcus faecalis". Science. 299 (5615): 2071–2074. Bibcode:2003Sci...299.2071P. doi:10.1126/science.1080613. ISSN 1095-9203. PMID 12663927. S2CID 45480495.
- ↑ Sheehan, M. M.; García, J. L.; López, R.; García, P. (1997-08-01). "The lytic enzyme of the pneumococcal phage Dp-1: a chimeric lysin of intergeneric origin". Molecular Microbiology. 25 (4): 717–725. doi: 10.1046/j.1365-2958.1997.5101880.x . ISSN 0950-382X. PMID 9379901. S2CID 37991956.
- ↑ "1.E.24 The Bacterophase Dp-1 Holin (Dp-1 Holin) Family". Transporter Classification Database. Retrieved 2016-03-28.
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