A Common Polymorphism in RNASE6 Impacts Its Antimicrobial Activity toward Uropathogenic Escherichia coli

Abstract

Human Ribonuclease (RNase) 6 is a monocyte and macrophage-derived protein with potent antimicrobial activity toward uropathogenic bacteria. The RNASE6 gene is heterogeneous in humans due to the presence of single nucleotide polymorphisms (SNPs). RNASE6 rs1045922 is the most common non-synonymous SNP, resulting in a G to A substitution that determines an arginine (R) to glutamine (Q) transversion at position 66 in the protein sequence. By structural analysis we observed that R66Q substitution significantly reduces the positive electrostatic charge at the protein surface. Here, we generated both recombinant RNase 6-R66 and -Q66 protein variants and determined their antimicrobial activity toward uropathogenic Escherichia coli (UPEC), the most common cause of UTI. We found that the R66 variant, encoded by the major SNP rs1045922 allele, exhibited superior bactericidal activity in comparison to the Q66 variant. The higher bactericidal activity of R66 variant correlated with an increase in the protein lipopolysaccharide binding and bacterial agglutination abilities, while retaining the same enzymatic efficiency. These findings encourage further work to evaluate RNASE6 SNP distribution and its impact in UTI susceptibility.

Murine Ribonuclease 6 Limits Bacterial Dissemination During Experimental Urinary Tract Infection

“…While mammalian genomes encode hundreds of AMPs [ 41 ], their cellular sources and functional significance remain largely untested in vivo. In a similar vein, RNase 6 is a highly evolutionarily conserved AMP with potent antimicrobial activity toward UPEC [ 23 , 24 , 26 ], but its physiological roles have remained uncertain. Accordingly, the dual purposes of this study were to (1) definitively establish the cellular sources of mouse Rnase6 in vivo and (2) test the hypothesis that Rnase6 serves an essential role in conferring antimicrobial activity toward UPEC.…”

“…RNase 6 is an evolutionarily conserved AMP expressed by leukocytes in patients with UTI and during murine experimental UTI [ 23 ]. Human and mouse RNase 6 kill UPEC at low micromolar concentrations without exerting cytotoxicity toward host cells [ 23 , 24 ]. Recently, we determined that human RNASE6 transgenic mice are protected from experimental UTI, consistent with the concept that future interventions to augment the level and/or activity of RNase 6 may reduce the incidence and severity of UTI [ 25 , 26 ].…”