AI Article Synopsis
- The Mnt repressor in Salmonella bacteriophage P22 plays a critical role in switching between lysogenic and lytic growth modes.
- Recent NMR spectroscopy determined the solution structure of its C-terminal tetramerization domain, revealing a complex arrangement of four alpha-helical subunits that form unique right-handed coiled coils.
- This structure demonstrates significant differences from typical coiled coils, including stronger superhelical winding and asymmetrical interactions between monomers, which enable dynamic interconversion over time.
Article Abstract
The tetrameric Mnt repressor is involved in the genetic switch between the lysogenic and lytic growth of Salmonella bacteriophage P22. The solution structure of its C-terminal tetramerization domain, which holds together the two dimeric DNA-binding domains, has been determined by NMR spectroscopy. This structure reveals an assembly of four alpha-helical subunits, consisting of a dimer of two antiparallel coiled coils with a unique right-handed twist. The superhelical winding is considerably stronger and the interhelical separation closer than those found in the well-known left-handed coiled coils in fibrous proteins and leucine zippers. An unusual asymmetry arises between the two monomers that comprise one right-handed coiled coil. A difference in the packing to the adjacent monomer of the other coiled coil occurs with an offset of two helical turns. The two asymmetric monomers within each coiled coil interconvert on a time scale of seconds. Both with respect to symmetry and handedness of helical packing, the C2 symmetric four-helix bundle of Mnt differs from other oligomerization domains that assemble DNA-binding modules, such as that in the tumor suppressor p53 and the E. coli lac repressor.
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