Hfq protein

The Hfq protein (also known as HF-I protein) encoded by the hfq gene was discovered in 1968 as an Escherichia. coli host factor that was essential for replication of the bacteriophage Qβ.[1] It is now clear that Hfq is an abundant bacterial RNA binding protein which has many important physiological roles. Usually mediated by interacting with Hfq binding sRNA.

In E. coli, Hfq mutants show multiple stress response related phenotypes.[2] The Hfq protein is now known to regulate the translation of two major stress transcription factors ( σS (RpoS) and σE (RpoE) ) in Enterobacteria.[3][4][5] It also regulates sRNA in Vibrio cholerae, a specific example being MicX sRNA.[6] In Salmonella typhimurium Hfq has been shown to be an essential virulence factor as its deletion attenuates the ability of S.typhimurium to invade epithelial cells, secrete virulence factors or survive in cultured macrophages.[7] In Salmonella Hfq deletion mutants are also non motile and exhibit chronic activation of the sigma mediated envelope stress response.[8]

Hfq mediates its plieotrophic effects through several mechanisms. It interacts with regulatory sRNA and facilitates their antisense interaction with their targets. Its also acts independently to modulate mRNA decay (directing mRNA transcripts for degradation) and also acts as a repressor of mRNA translation. Genomic SELEX has been used to show that Hfq binding RNAs are enriched in the sequence motif 5'-AAYAAYAA-3'.[9]

Electron microscopy imaging reveals that, in addition to the expected localization of this protein in cytoplasmic regions and in the nucleoid, an important fraction of Hfq is located in close proximity to the membrane.[10]

Crystallographic structures

Six crystallographic structures of 4 different Hfq proteins have been published so far; E. coli Hfq (PDB 1HK9), P. aeruginosa Hfq in a low salt condition (1U1S) and a high salt condition (1U1T), Hfq from S. aureus with bound RNA (1KQ2) and without (1KQ1), and the Hfq(-like) protein from M. jannaschii (2QTX).

All six structures confirm the hexameric ring-shape of a Hfq protein complex.

References

  1. ^ August JT, Eoyang L, De Fernandez MT, et al. (1970). "Phage-specific and host proteins in the replication of bacteriophage RNA". Fed. Proc. 29 (3): 1170–5. PMID 4315363. 
  2. ^ Tsui HC, Leung HC, Winkler ME (July 1994). "Characterization of broadly pleiotropic phenotypes caused by an hfq insertion mutation in Escherichia coli K-12". Molecular microbiology 13 (1): 35–49. doi:10.1111/j.1365-2958.1994.tb00400.x. PMID 7984093. 
  3. ^ Muffler A, Fischer D, Hengge-Aronis R (May 1996). "The RNA-binding protein HF-I, known as a host factor for phage Qbeta RNA replication, is essential for rpoS translation in Escherichia coli". Genes & development 10 (9): 1143–51. doi:10.1101/gad.10.9.1143. PMID 8654929. http://www.genesdev.org/cgi/pmidlookup?view=long&pmid=8654929. 
  4. ^ Guisbert E, Rhodius VA, Ahuja N, Witkin E, Gross CA (March 2007). "Hfq modulates the sigmaE-mediated envelope stress response and the sigma32-mediated cytoplasmic stress response in Escherichia coli". Journal of bacteriology 189 (5): 1963–73. doi:10.1128/JB.01243-06. PMC 1855744. PMID 17158661. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1855744. 
  5. ^ Brown L, Elliott T (July 1996). "Efficient translation of the RpoS sigma factor in Salmonella typhimurium requires host factor I, an RNA-binding protein encoded by the hfq gene". Journal of bacteriology 178 (13): 3763–70. PMC 232634. PMID 8682778. http://jb.asm.org/cgi/pmidlookup?view=long&pmid=8682778. 
  6. ^ Davis BM, Waldor MK (July 2007). "RNase E-dependent processing stabilizes MicX, a Vibrio cholerae sRNA". Mol. Microbiol. 65 (2): 373–85. doi:10.1111/j.1365-2958.2007.05796.x. PMC 1976385. PMID 17590231. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1976385. Retrieved 2010-07-22. 
  7. ^ Sittka A, Pfeiffer V, Tedin K, Vogel J (January 2007). "The RNA chaperone Hfq is essential for the virulence of Salmonella typhimurium". Molecular microbiology 63 (1): 193–217. doi:10.1111/j.1365-2958.2006.05489.x. PMC 1810395. PMID 17163975. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1810395. 
  8. ^ Figueroa-Bossi N, Lemire S, Maloriol D, Balbontín R, Casadesús J, Bossi L (November 2006). "Loss of Hfq activates the sigmaE-dependent envelope stress response in Salmonella enterica". Molecular microbiology 62 (3): 838–52. doi:10.1111/j.1365-2958.2006.05413.x. PMID 16999834. 
  9. ^ Lorenz C, Gesell T, Zimmermann B, Schoeberl U, Bilusic I, Rajkowitsch L, Waldsich C, von Haeseler A, Schroeder R (2010). "Genomic SELEX for Hfq-binding RNAs identifies genomic aptamers predominantly in antisense transcripts.". Nucleic Acids Res 38 (11): 3794–808. doi:10.1093/nar/gkq032. PMC 2887942. PMID 20348540. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2887942. 
  10. ^ Diestra E, Cayrol B, Arluison V, Risco C. (2009). Mayer, Claudine. ed. "Cellular electron microscopy imaging reveals the localization of the Hfq protein close to the bacterial membrane.:". PLoS One. 4 (12): e8301. doi:10.1371/journal.pone.0008301. PMC 2789413. PMID 20011543. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2789413. 

External links

B bsyn: dna (repl, cycl, reco, repr) · tscr (fact, tcrg, nucl, rnat, rept, ptts) · tltn (risu, pttl, nexn) · dnab, rnab/runp · stru (domn, 1°, 2°, 3°, 4°)