TY - JOUR
T1 - High-resolution crystal structure of the restriction–modification controller protein C.AhdI from Aeromonas hydrophila
AU - McGeehan, John
AU - Streeter, Simon
AU - Papapanagiotou, I.
AU - Fox, G.
AU - Kneale, Geoff
PY - 2005
Y1 - 2005
N2 - Restriction–modification (R–M) systems serve to protect the host bacterium from invading bacteriophage. The multi-component system includes a methyltransferase, which recognizes and methylates a specific DNA sequence, and an endonuclease which recognises the same sequence and cleaves within or close to this site. The endonuclease will only cleave DNA that is unmethylated at the specific site, thus host DNA is protected while non-host DNA is cleaved. However, following DNA replication, expression of the endonuclease must be delayed until the host DNA is appropriately methylated. In many R–M systems, this regulation is achieved at the transcriptional level via the controller protein, or C-protein.
We have solved the first X-ray structure of an R–M controller protein, C.AhdI, to 1.69 Å resolution using selenomethionine MAD. C.AhdI is part of a Type IIH R–M system from the pathogen Aeromonas hydrophila. The structure reveals an all-α protein that contains a classical helix-turn-helix (HTH) domain and can be assigned to the Xre family of transcriptional regulators. Unlike its monomeric structural homologues, an extended helix generates an interface that results in dimerisation of the free protein. The dimer is electrostatically polarised and a positively charged surface corresponds to the position of the DNA recognition helices of the HTH domain. Comparison with the structure of the λ cI ternary complex suggests that C.AhdI activates transcription through direct contact with the σ70 subunit of RNA polymeras
AB - Restriction–modification (R–M) systems serve to protect the host bacterium from invading bacteriophage. The multi-component system includes a methyltransferase, which recognizes and methylates a specific DNA sequence, and an endonuclease which recognises the same sequence and cleaves within or close to this site. The endonuclease will only cleave DNA that is unmethylated at the specific site, thus host DNA is protected while non-host DNA is cleaved. However, following DNA replication, expression of the endonuclease must be delayed until the host DNA is appropriately methylated. In many R–M systems, this regulation is achieved at the transcriptional level via the controller protein, or C-protein.
We have solved the first X-ray structure of an R–M controller protein, C.AhdI, to 1.69 Å resolution using selenomethionine MAD. C.AhdI is part of a Type IIH R–M system from the pathogen Aeromonas hydrophila. The structure reveals an all-α protein that contains a classical helix-turn-helix (HTH) domain and can be assigned to the Xre family of transcriptional regulators. Unlike its monomeric structural homologues, an extended helix generates an interface that results in dimerisation of the free protein. The dimer is electrostatically polarised and a positively charged surface corresponds to the position of the DNA recognition helices of the HTH domain. Comparison with the structure of the λ cI ternary complex suggests that C.AhdI activates transcription through direct contact with the σ70 subunit of RNA polymeras
U2 - 10.1016/j.jmb.2004.12.025
DO - 10.1016/j.jmb.2004.12.025
M3 - Article
SN - 0022-2836
VL - 346
SP - 689
EP - 701
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 3
ER -