Part:BBa_K1378031

Holin from lambda phage

Holin is a 105-amino-acid-residue cytoplasmic membrane protein with three transmembrane domains, naturally expressed by double-stranded lambada phage. Holin will oligomerize and form a hole on the inner membrane of host bacteria at a certain time at an allele-specific time. And then the formation of hole will help Endolysin, a kind of lysozyme, come out from cytoplasm to periplasm to degrade peptidoglycan and inhibit the respiration by eliminating proton gradient.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

Usage and Biology

Holin is a generic term to describe a group of small proteins produced by double-stranded DNA bacteriophage to trigger holes formation at the end of lytic cycle. In our project, we design our suicide switch based on the λ lysis model. The S holin, also called S₁₀₅, encoded by S gene, a dual-start motif of λ phage, is an 105-amino-acid-residue CM protein with three transmembrane domains (TMD)^[1]. S₁₀₇, also called antiholin, is the other protein encoded by S gene, differing from the S holin only by the Met-Lys N-terminal extension. However, this difference confers to S₁₀₇ an extra positive charge, which prevents its TMD1 from inserting into the CM^[2]. Additionally, as its name suggests, S₁₀₇ can bind to S105 and inhibit its function specifically^[3]. In λ lysis system, S₁₀₇ and S₁₀₅ are encoded by S gene at ratio of approximately 1:2, which is defined by the two RNA structure, and if the amount of S₁₀₇ is increased relative to S₁₀₅, the 'lysis time' will be delayed^[4]. The inhibition function of S₁₀₇ can be subverted by collapsing proton motive force, which also allow insertion of TMD1 of S₁₀₇ into CM, instantly increasing the amount of active holin by making previously inactive S₁₀₇ - S₁₀₅ complexes functional (Fig. 1).

Figure 1. The model for the membrane topology of S₁₀₇ and S₁₀₅. S₁₀₅ consist of three transmembrane domains (TMD) with an N-out, C-in topology while S₁₀₇ only has two TMDs, caused by an extra positive charge conferred by Lys2. The S₁₀₇ can inhibit the function of S₁₀₅, preventing it from forming holes in cell membrane. However, this inhibition can be subverted by the dissipation of proton motive force and in this case, S₁₀₇ will become active holin, accelerating the rate of pore formation.

Reference

[1]Gründling, A., Bläsi, U., & Young, R. (2000). Biochemical and genetic evidence for three transmembrane domains in the class I holin, lambda S. Journal of Biological Chemistry, 275(2), 769-776.

[2]Young, R., Wang, I. N., & Roof, W. D. (2000). Phages will out: strategies of host cell lysis. Trends in microbiology, 8(3), 120-128.

[3]Bläsi, U., Chang, C. Y., Zagotta, M. T., Nam, K. B., & Young, R. (1990). The lethal lambda S gene encodes its own inhibitor. The EMBO journal, 9(4), 981.

[4]Bläsi, U., Nam, K., Hartz, D., Gold, L., & Young, R. (1989). Dual translational initiation sites control function of the lambda S gene. The EMBO journal, 8(11), 3501.