Hfqs in Bacillus anthracis: Role of protein sequence variation in the structure and function of proteins in the Hfq family.
Hfq proteins in Gram-negative bacteria play important roles in bacterial physiology and virulence, mediated by binding of the Hfq hexamer to small RNAs and/or mRNAs to post-transcriptionally regulate gene expression. However, the physiological role of Hfqs in Gram-positive bacteria is less clear. Bacillus anthracis, the causative agent of anthrax, uniquely expresses three distinct Hfq proteins, two from the chromosome (Hfq1, Hfq2) and one from its pXO1 virulence plasmid (Hfq3). The protein sequences of Hfq1 and 3 are evolutionarily distinct from those of Hfq2 and of Hfqs found in other Bacilli. Here, the quaternary structure of each B. anthracis Hfq protein, as produced heterologously in Escherichia coli, was characterized. While Hfq2 adopts the expected hexamer structure, Hfq1 does not form similarly stable hexamers in vitro. The impact on the monomer-hexamer equilibrium of varying Hfq C-terminal tail length and other sequence differences among the Hfqs was examined, and a sequence region of the Hfq proteins that was involved in hexamer formation was identified. It was found that, in addition to the distinct higher-order structures of the Hfq homologs, they give rise to different phenotypes. Hfq1 has a disruptive effect on the function of E. coli Hfq in vivo, while Hfq3 expression at high levels is toxic to E. coli but also partially complements Hfq function in E. coli. These results set the stage for future studies of the roles of these proteins in B. anthracis physiology and for the identification of sequence determinants of phenotypic complementation.
NIAID, National Institutes of Health (NIH), 33 North Drive, Bethesda, Maryland.
Catherine
C
Vrentas
NIDDK, NIH, 5 Memorial Drive, Bethesda, Maryland.
Rodolfo
R
Ghirlando
NIAID, National Institutes of Health (NIH), 33 North Drive, Bethesda, Maryland.
Andrea
A
Keefer
NIAID, National Institutes of Health (NIH), 33 North Drive, Bethesda, Maryland.
Zonglin
Z
Hu
NIAID, NIH, 10 Center Drive, Bethesda, Maryland.
Aurelie
A
Tomczak
Structural Biology Section, Research Technologies Branch, NIAID, NIH, Twinbrook II, 12441 Parklawn Drive, Rockville, Maryland.
Apostolos G
AG
Gittis
NIAID, National Institutes of Health (NIH), 33 North Drive, Bethesda, Maryland.
Athulaprabha
A
Murthi
Structural Biology Section, Research Technologies Branch, NIAID, NIH, Twinbrook II, 12441 Parklawn Drive, Rockville, Maryland.
David N
DN
Garboczi
NCI, NIH, 37 Convent Drive, Bethesda, MD.
Susan
S
Gottesman
NIAID, National Institutes of Health (NIH), 33 North Drive, Bethesda, Maryland.
Stephen H
SH
Leppla
D000595:Amino Acid Sequence; D001408:Bacillus anthracis / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D035001:Host Factor 1 Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
D035001:Host Factor 1 Protein; D011994:Recombinant Proteins
Bacillus anthracis; Hfq; anthrax; pXO1; sRNA; small RNA