T4 holin explained

The T4 Holin Family (TC# 1.E.8) 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 (Lysozyme E) was identified in 1961, the holin (product of gene t and called T-holin) was not characterized until 2001.[1] A representative list of proteins belonging to the T4 holin family can be found in the Transporter Classification Database.[2]

Structure

T4 holin is fairly large, about 218 amino acyl residues (aas) in length. The protein is highly hydrophilic with 49 acidic and basic residues distributed along its length and a single putative transmembrane segment (TMS) near its N-terminus, leaving most of the protein in the periplasm.[3]

Function

The large periplasmic domain is a major determinant in the timing mechanism and is involved in lysis inhibition (LIN).[4] LIN involves the antiholin rI protein of T4 (See TC# 1.E.8.1.1).[5] Lysis inhibition is an effective strategy to coordinate lysis timing with phage particle maturation and to exclude other phage.[6] The C-terminal periplasmic domain of T4 holin binds the periplasmic domain of T4 antiholin (RI; 97 aas) which like the holin, spans the membrane once. T-holin of T4 phage forms a 1:1 complex with the RI inhibitor which block aggregation and pore formation.[7]

Homology

The phage T4 T-holin (lysis protein) is identical to the holin from phage K3 and nearly identical to that from phage ARI. Residues 35-96 are 28% identical to residues 436-495 of a K+ uptake protein of Lactococcus lactis (gbAAK04721; TC# 2.A.72; KUP), suggesting an evolutionary relationship between a holin and a transporter. Holins have 1 to 4 TMSs and a short C-terminal domain rich in basic residues.

See also

Further reading

Notes and References

  1. Ramanculov . E. . Young . R. . 2001-04-01 . Functional analysis of the phage T4 holin in a lambda context . Molecular Genetics and Genomics . 265 . 2 . 345–353 . 1617-4615 . 11361346 . 10.1007/s004380000422. 40455691 .
  2. Web site: 1.E.8 The T4 Holin (T4 Holin) Family. Transporter Classification Database. 2016-03-26.
  3. Tran . Tram Anh T. . Struck . Douglas K. . Young . Ry . 2005-10-01 . Periplasmic domains define holin-antiholin interactions in t4 lysis inhibition . Journal of Bacteriology . 187 . 19 . 6631–6640 . 10.1128/JB.187.19.6631-6640.2005 . 0021-9193 . 1251592 . 16166524.
  4. Ramanculov . E. . Young . R. . 2001-03-07 . Genetic analysis of the T4 holin: timing and topology . Gene . 265 . 1–2 . 25–36 . 0378-1119 . 11255004 . 10.1016/s0378-1119(01)00365-1.
  5. Ramanculov . E. . Young . R. . 2001-08-01 . An ancient player unmasked: T4 rI encodes a t-specific antiholin . Molecular Microbiology . 41 . 3 . 575–583 . 0950-382X . 11532126 . 10.1046/j.1365-2958.2001.02491.x. 25273199 . free .
  6. Miller . Eric S. . Kutter . Elizabeth . Mosig . Gisela . Arisaka . Fumio . Kunisawa . Takashi . Rüger . Wolfgang . 2003-03-01 . Bacteriophage T4 genome . Microbiology and Molecular Biology Reviews . 67 . 1 . 86–156, table of contents . 1092-2172 . 150520 . 12626685 . 10.1128/mmbr.67.1.86-156.2003.
  7. Moussa . Samir H. . Kuznetsov . Vladimir . Tran . Tram Anh T. . Sacchettini . James C. . Young . Ry . 2012-04-01 . Protein determinants of phage T4 lysis inhibition . Protein Science . 21 . 4 . 571–582 . 10.1002/pro.2042 . 1469-896X . 3375757 . 22389108.

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