Insights into the CtrA regulon in development of stress resistance in obligatory intracellular pathogen Ehrlichia chaffeensis

Abstract

Summary Ehrlichia chaffeensis is an obligate intracellular bacterium that causes human monocytic ehrlichiosis. Ehrlichiae have a biphasic developmental cycle consisting of dense-cored cells (DCs) and reticulate cells (RCs). Isolated DCs are more stress resistant and infectious than RCs. Here, we report that a response regulator, CtrA was upregulated in human monocytes at the late growth stage when DCs develop. E. chaffeensis CtrA bound to the promoters of late-stage transcribed genes: ctrA, ompA (peptidoglycan-associated lipoprotein), bolA (stress-induced morphogen), and surE (stationary phase survival protein), which contain CtrA-binding motifs, and transactivated ompA, surE, and bolA promoter-lacZ fusions in Escherichia coli. OmpA was predominantly expressed in DCs. E. chaffeensis binding to and subsequent infection of monocytes were inhibited by anti-OmpA IgG. E. chaffeensis BolA bound to the promoters of genes encoding outer surface proteins TRP120 and ECH_1038, which were expressed in DCs, and transactivated trp120 and ECH_1038 promoter-lacZ fusions. E. chaffeensis bolA complemented a stress-sensitive E. coli bolA mutant. E. coli expressing E. chaffeensis surE exhibited increased resistance to osmotic stress. Our results suggest that E. chaffeensis CtrA plays a role in coordinating development of the stress resistance for passage from the present to the next host cells through its regulon.

Structural and Spectroscopic Insights into BolA-Glutaredoxin Complexes

“…The Helix-turn-helix (HTH) Motif of BolAs Is Potentially Involved in DNA Binding-Currently, only bacterial BolA_H members have been shown to act as transcriptional regulators by binding to gene promoters (34,35), whereas Uvi31ϩ, a BolA_H from Chlamydomonas reinhardtii, likely exhibits endonuclease activity (36). The capacity to bind nucleic acids is in line with the fact that BolA possesses an overall fold related to the one found in type II K-homology (KH) domain-containing proteins (33) known to bind nucleic acids.…”

Anaplasma marginale Outer Membrane Protein A Is an Adhesin That Recognizes Sialylated and Fucosylated Glycans and Functionally Depends on an Essential Binding Domain

“…Given its demonstrated role in AmOmpA and ApOmpA function, K58 might contribute to the adhesin capabilities of all Anaplasma and Ehrlichia species OmpA proteins. Our findings presented here, together with a previous report that E. chaffeensis OmpA contributes to infection of monocytic cells (19), prompt us to propose that ehrlichial OmpA proteins also are adhesins that contribute to cellular invasion and do so by recognizing sialylated and fucosylated glycans in a manner that involves the conserved lysine.…”

“…Given the demonstrated roles of A. phagocytophilum and E. chaffeensis OmpA proteins in promoting infection of mammalian host cells (17,19,21), we sought to determine if AmOmpA performs a similar adhesin function for A. marginale. An alignment of ApOmpA and AmOmpA revealed that the two exhibit 52.33% sequence identity (17).…”

“…OmpA is highly conserved among A. marginale sensu stricto strains and isolates, exhibiting 99.6 to 100% identity (14). Clues pertaining to the role of A. marginale OmpA (AmOmpA) are provided by recent studies demonstrating the importance of OmpA proteins to cellular invasion by A. phagocytophilum and Ehrlichia chaffeensis, two Anaplasmataceae members that cause potentially fatal infections of humans and animals (17)(18)(19). Indeed, we discovered that A. phagocytophilum OmpA (ApOmpA) is one of a trio of adhesins that cooperatively function to mediate optimal bacterial binding to and invasion of host cells (17,18,20,21).…”

“…Antibodies raised against full-length ApOmpA or its 16-residue binding domain inhibit A. phagocytophilum infection of host cells (18). Likewise, antibodies against E. chaffeensis OmpA inhibit ehrlichial infection in vitro (19).…”