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by Keyword: HHA


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Solórzano, Carla, Srikumar, Shabarinath, Canals, Rocío, Juárez, Antonio, Paytubi, Sonia, Madrid, Cristina, (2015). Hha has a defined regulatory role that is not dependent upon H-NS or StpA Frontiers in Microbiology 6, Article 773

The Hha family of proteins is involved in the regulation of gene expression in enterobacteria by forming complexes with H-NS-like proteins. Whereas several amino acid residues of both proteins participate in the interaction, some of them play a key role. Residue D48 of Hha protein is essential for the interaction with H-NS, thus the D48N substitution in Hha protein abrogates H-NS/Hha interaction. Despite being a paralog of H-NS protein, StpA interacts with HhaD48N with higher affinity than with the wild type Hha protein. To analyze whether Hha is capable of acting independently of H-NS and StpA, we conducted transcriptomic analysis on the hha and stpA deletion strains and the hhaD48N substitution strain of Salmonella Typhimurium using a custom microarray. The results obtained allowed the identification of 120 genes regulated by Hha in an H-NS/StpA-independent manner, 38% of which are horizontally acquired genes. A significant number of the identified genes are involved in functions related to cell motility, iron uptake, and pathogenicity. Thus, motility assays, siderophore detection and intra-macrophage replication assays were performed to confirm the transcriptomic data. Our findings point out the importance of Hha protein as an independent regulator in S. Typhimurium, highlighting a regulatory role on virulence.

Keywords: Salmonella, Gene regulation, Motility, Pathogenicity island, H-NS, HHA, STPA


Paytubia, S., Dietrich, M., Queiroz, M.H., Juárez, A., (2013). Role of plasmid- and chromosomally encoded Hha proteins in modulation of gene expression in E. coli O157:H7 Plasmid International Society for Plasmid Biology Meeting , Elsevier (Santander, Spain) 70 (1), 52-60

H-NS and Hha belong to the nucleoid-associated family of proteins and modulate gene expression in response to environmental stimuli. Genes coding for these proteins can be either chromosomally or plasmid-encoded. In this work, we analyse the regulatory role of the Hha protein encoded in the virulence plasmid of the enterohemorrhagic Escherichia coli O157:H7 (HhapO157). This plasmid is present in all clinical isolates of E. coli O157:H7 and contributes to virulence. Both, HhapO157 and E. coli O157:H7-chromosomal Hha (Hhachr) exhibit a significant degree of similarity. The hha gene from plasmid pO157 is transcribed from its own putative promoter and is overexpressed in a chromosomal hha mutant. As its chromosomal counterpart, HhapO157 is able to interact with H-NS. Remarkably, HhapO157 targets only a subset of the genes modulated by Hhachr. This has been evidenced by both assaying the ability of HhapO157 to complement expression of a specific operon (i.e., the haemolysin operon) and by comparing the global transcriptome of the wt strain and its hhap, hhac and hhapc mutant derivatives. HhapO157 and Hhachr share some common regulatory features, however they also display specific targeting of some genes and even a different modulatory role in some others.

Keywords: E. coli O157:H7, Hha, H-NS, Plasmid, pO157, Nucleoid-associated proteins


de Alba, C. F., Solorzano, C., Paytubi, S., Madrid, C., Juarez, A., Garcia, J., Pons, M., (2011). Essential residues in the H-NS binding site of Hha, a co-regulator of horizontally acquired genes in Enterobacteria FEBS Letters , 585, (12), 1765-1770

Proteins of the Hha/YmoA family co-regulate with H-NS the expression of horizontally acquired genes in Enterobacteria. Systematic mutations of conserved acidic residues in Hha have allowed the identification of D48 as an essential residue for H-NS binding and the involvement of E25. Mutations of these residues resulted in deregulation of sensitive genes in vivo. D48 is only partially solvent accessible, yet it defines the functional binding interface between Hha and H-NS confirming that Hha has to undergo a conformational change to bind H-NS. Exposed acidic residues, such as E25, may electrostatically facilitate and direct the approach of Hha to the positively charged region of H-NS enabling the formation of the final complex when D48 becomes accessible by a conformational change of Hha. Structured summary of protein interactions: YdgT and H-NS bind by nuclear magnetic resonance (View interaction) Hha and H-NS bind by nuclear magnetic resonance (View Interaction 1, 2, 3) Hha physically interacts with H-NS by pull down (View Interaction 1, 2).

Keywords: Nucleoid associated protein, H-NS, Hha, Transcription repression


Paytubi, S., Garcia, J., Juarez, A., (2011). Bacterial Hha-like proteins facilitate incorporation of horizontally transferred DNA Central European Journal of Biology , 6, (6), 879-886

Horizontal gene transfer (HGT), non-hereditary transfer of genetic material between organisms, accounts for a significant proportion of the genetic variability in bacteria. In Gram negative bacteria, the nucleoid-associated protein H-NS silences unwanted expression of recently acquired foreign DNA. This, in turn, facilitates integration of the incoming genes into the regulatory networks of the recipient cell. Bacteria belonging to the family Enterobacteriaceae express an additional protein, the Hha protein that, by binding to H-NS, potentiates silencing of HGT DNA. We provide here an overview of Hha-like proteins, including their structure and function, as well as their evolutionary relationship. We finally present available information suggesting that, by expressing Hha-like proteins, bacteria such as Escherichia coli facilitate HGT incorporation and hence, the impact of HGT in their genetic diversity.

Keywords: Hha, H-NS, HGT DNA, Enterobacteria, Nucleoid-associated proteins, Enterica serovar typhimurium, Histone-like protein, h-ns, Escherichia-coli, Yersinia-enterocolitica, Salmonella-enterica


Banos, R. C., Vivero, A., Aznar, S., Garcia, J., Pons, M., Madrid, C., Juarez, A., (2009). Differential regulation of horizontally acquired and core genome genes by the bacterial modulator H-NS PLoS Genetics , 5, (6), 8

Horizontal acquisition of DNA by bacteria dramatically increases genetic diversity and hence successful bacterial colonization of several niches, including the human host. A relevant issue is how this newly acquired DNA interacts and integrates in the regulatory networks of the bacterial cell. The global modulator H-NS targets both core genome and HGT genes and silences gene expression in response to external stimuli such as osmolarity and temperature. Here we provide evidence that H-NS discriminates and differentially modulates core and HGT DNA. As an example of this, plasmid R27-encoded H-NS protein has evolved to selectively silence HGT genes and does not interfere with core genome regulation. In turn, differential regulation of both gene lineages by resident chromosomal H-NS requires a helper protein: the Hha protein. Tight silencing of HGT DNA is accomplished by H-NS-Hha complexes. In contrast, core genes are modulated by H-NS homoligomers. Remarkably, the presence of Hha-like proteins is restricted to the Enterobacteriaceae. In addition, conjugative plasmids encoding H-NS variants have hitherto been isolated only from members of the family. Thus, the H-NS system in enteric bacteria presents unique evolutionary features. The capacity to selectively discriminate between core and HGT DNA may help to maintain horizontally transmitted DNA in silent form and may give these bacteria a competitive advantage in adapting to new environments, including host colonization.

Keywords: 2A strain 2457T, Escherichia-Coli, Salmonella-Enterica, Protein, DNA, Expression, Binding, HHA, Shigella, Plasmid


Garcia, J., Madrid, C., Cendra, M., Juarez, A., Pons, M., (2009). N9L and L9N mutations toggle Hha binding and hemolysin regulation by Escherichia coli and Vibrio cholerae H-NS FEBS Letters , 583, (17), 2911-2916

Proteins of the Hha/YmoA family co-regulate with H-NS the expression of virulence factors in Enterobacteriaceae. Vibrio cholerae lacks Hha-like proteins and its H-NS (vcH-NS) is unable to bind Hha, in spite of the conservation of a key residue for Hha binding by Escherichia coli H-NS (ecH-NS). Exchange of the residues in position 9 between vcH-NS and ecH-NS strongly reduces Hha binding by ecH-NS and introduces it in vcH- NS. These mutations strongly affect the repression of the hemolysin operon in E. coli and the electrophoretic mobility of complexes formed with a DNA fragment containing its regulatory region.

Keywords: Nucleoid associated protein, H-NS, Hha, Transcription repression, NMR, Electrophoretic mobility shift assays


Cordeiro, Tiago N., García, Jesús, Pons, José-Ignacio, Aznar, Sonia, Juárez, Antonio, Pons, Miquel, (2008). A single residue mutation in Hha preserving structure and binding to H-NS results in loss of H-NS mediated gene repression properties FEBS Letters , 582, (20), 3139-3144

In this study, we report that a single mutation of cysteine 18 to isoleucine (C18I) in Escherichia coli Hha abolishes the repression of the hemolysin operon observed in the wild-type protein. The phenotype also includes a significant decrease in the growth rate of E. coli cells at low ionic strength. Other substitutions at this position (C18A, C18S) have no observable effects in E. coli growth or hemolysin repression. All mutants are stable and well folded and bind H-NS in vitro with similar affinities suggesting that Cys 18 is not directly involved in H-NS binding but this position is essential for the activity of the H-NS/Hha heterocomplexes in the regulation of gene expression.

Keywords: Nucleoid-associated protein, H-NS, Hha, Transcription repression


Castellarnau, Marc, Errachid, Abdelhamid, Madrid, Cristina, Juárez, Antonio, Samitier, Josep, (2006). Dielectrophoresis as a tool to characterize and differentiate isogenic mutants of Escherichia coli Biophysical Journal , 91, (10), 3937-3945

In this study we report on an experimental method based on dielectrophoretic analysis to identify changes in four Escherichia coli isogenic strains that differed exclusively in one mutant allele. The dielectrophoretic properties of wild-type cells were compared to those of hns, hha, and hha hns mutant derivatives. The hns and hha genes code respectively for the global regulators Hha and H-NS. The Hha and H-NS proteins modulate gene expression in Escherichia coli and other Gram negative bacteria. Mutations in either hha or hns genes result in a pleiotropic phenotype. A two-shell prolate ellipsoidal model has been used to fit the experimental data, obtained from dielectrophoresis measurements, and to study the differences in the dielectric properties of the bacterial strains. The experimental results show that the mutant genotype can be predicted from the dielectrophoretic analysis of the corresponding cultures, opening the way to the development of microdevices for specific identification. Therefore, this study shows that dielectrophoresis can be a valuable tool to study bacterial populations which, although apparently homogeneous, may present phenotypic variability.

Keywords: H-NS, Dielectric behaviour, Hemolysin genes, Cells, Separation, Expression, Proteins, HHA, Electrorotation, Polarization