X-ray crystal structure of the bacterial conjugation factor PsiB, a negative regulator of RecA.
During bacterial conjugation, genetic material from one cell is transferred to another as single-stranded DNA. The introduction of single-stranded DNA into the recipient cell would ordinarily trigger a potentially deleterious transcriptional response called SOS, which is initiated by RecA protein filaments formed on the DNA. During F plasmid conjugation, however, the SOS response is suppressed by PsiB, an F-plasmid-encoded protein that binds and sequesters free RecA to prevent filament formation. Among the many characterized RecA modulator proteins, PsiB is unique in using sequestration as an inhibitory mechanism. We describe the crystal structure of PsiB from the Escherichia coli F plasmid. The stucture of PsiB is surprisingly similar to CapZ, a eukaryotic actin filament capping protein. Structure-directed neutralization of electronegative surfaces on PsiB abrogates RecA inhibition whereas neutralization of an electropositive surface element enhances PsiB inhibition of RecA. Together, these studies provide a first molecular view of PsiB and highlight its use as a reagent in studies of RecA activity.
Petrova
Vessela
V
University of Wisconsin, Madison, Wisconsin 53706-1532, USA.
Satyshur
Kenneth A
KA
George
Nicholas P
NP
McCaslin
Darrell
D
Cox
Michael M
MM
Keck
James L
JL
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D051347:CapZ Actin Capping Protein / Q000737:chemistry; D003227:Conjugation, Genetic / Q000502:physiology; D018360:Crystallography, X-Ray; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry* / Q000378:metabolism; D005144:F Factor / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011938:Rec A Recombinases; D013014:SOS Response, Genetics / Q000502:physiology; D040681:Structural Homology, Protein
D001426:Bacterial Proteins; D051347:CapZ Actin Capping Protein; D004277:DNA, Single-Stranded; C058074:PsiB protein, Bacteria; D011938:Rec A Recombinases