Molecular and Structural Characterization of a Novel Escherichia coli Interleukin Receptor Mimic Protein

Abstract

Urinary tract infection (UTI) is a disease of extremely high incidence in both community and nosocomial settings. UTIs cause significant morbidity and mortality, with approximately 150 million cases globally per year. Uropathogenic Escherichia coli (UPEC) is the primary cause of UTI and is generally treated empirically. However, the rapidly increasing incidence of UTIs caused by multidrug-resistant UPEC strains has led to limited available treatment options and highlights the urgent need to develop alternative treatment and prevention strategies. In this study, we performed a comprehensive analysis to define the regulation, structure, function, and immunogenicity of recently identified UPEC vaccine candidate C1275 (here referred to as IrmA). We showed that the irmA gene is highly prevalent in UPEC, is cotranscribed with the biofilm-associated antigen 43 gene, and is regulated by the global oxidative stress response OxyR protein. Localization studies identified IrmA in the UPEC culture supernatant. We determined the structure of IrmA and showed that it adopts a unique domain-swapped dimer architecture. The dimeric structure of IrmA displays similarity to those of human cytokine receptors, including the interleukin-2 receptor (IL-2R), interleukin-4 receptor (IL-4R), and interleukin-10 receptor (IL-10R) binding domains, and we showed that purified IrmA can bind to their cognate cytokines. Finally, we showed that plasma from convalescent urosepsis patients contains high IrmA antibody titers, demonstrating the strong immunogenicity of IrmA. Taken together, our results indicate that IrmA may play an important role during UPEC infection.

Functional and structural characteristics of bacterial proteins that bind host cytokines

“…1B ). 7 This dimer has structural similarity with the extracellular binding domains of human cytokine receptors IL-2R and IL-4R and to lesser extent with IL-10R. Indeed, IrmA has been shown to interact with the corresponding cytokines IL-2, IL-4 and IL-10.…”

“…Indeed, IrmA has been shown to interact with the corresponding cytokines IL-2, IL-4 and IL-10. 7 Typically, the structural conformation involved in the formation of the IrmA dimer is more common in the formation of fibers such as those in the Ig-fold of fimbrial subunits. 43 The extracellular protein IrmA was first identified in studies seeking novel vaccine antigens to protect against E. coli sepsis in mice.…”

“… 44 Later, it was found that IrmA is regulated by the stress response protein OxyR, which represses the transcription of IrmA together with biofilm-associated antigen in uropathogenic E. coli (UPEC). 7 The amino acid sequence of IrmA is conserved, with 97% identity between strains, and the gene encoding IrmA can be found in most sequenced UPEC strains. 7 The fact that the serum of urosepsis patients infected with IrmA-positive UPEC strains has higher levels of IrmA-specific antibodies than the serum of healthy controls shows that IrmA has immunogenic potential in vivo .…”

“… 7 The amino acid sequence of IrmA is conserved, with 97% identity between strains, and the gene encoding IrmA can be found in most sequenced UPEC strains. 7 The fact that the serum of urosepsis patients infected with IrmA-positive UPEC strains has higher levels of IrmA-specific antibodies than the serum of healthy controls shows that IrmA has immunogenic potential in vivo . 7 …”

“… 2,4-7 However, the known bacterial cytokine-binding proteins represent a rather versatile group of proteins, including a channel-forming usher protein, 2 a gram-negative secretin, 6 an outer membrane pore protein, 5 a pilus subunit, 6 an intrinsically disordered outer membrane lipoprotein, 13 and a secreted protein displaying structural similarity to human cytokine receptors. 7 In addition to bacteria, viruses have also been reported to possess receptors for host cytokines (for a review, see ref. 14 ).…”