Ribonucleases as a host-defence family: evidence of evolutionarily conserved antimicrobial activity at the N-terminus

Abstract

Vertebrate secreted RNases (ribonucleases) are small proteins that play important roles in RNA metabolism, angiogenesis or host defence. In the present study we describe the antimicrobial properties of the N-terminal domain of the hcRNases (human canonical RNases) and show that their antimicrobial activity is well conserved among their lineage. Furthermore, all domains display a similar antimicrobial mechanism, characterized by bacteria agglutination followed by membrane permeabilization. The results of the present study show that, for all antimicrobial hcRNases, (i) activity is retained at the N-terminus and (ii) the antimicrobial mechanism is conserved. Moreover, using computational analysis we show that antimicrobial propensity may be conserved at the N-terminus for all vertebrate RNases, thereby suggesting that a defence mechanism could be a primary function in vertebrate RNases and that the N-terminus was selected to ensure this property. In a broader context, from the overall comparison of the peptides' physicochemical and biological properties, general correlation rules could be drawn to assist in the structure-based development of antimicrobial agents.

A Novel RNase 3/ECP Peptide for Pseudomonas aeruginosa Biofilm Eradication That Combines Antimicrobial, Lipopolysaccharide Binding, and Cell-Agglutinating Activities

“…No activity was detected under the same assayed conditions for pure neutral vesicles (data not shown), as previously observed for RNase 3 (41). The data also confirmed that the cell agglutination was specific for the tested Gram-negative species, as previously reported for the other assayed RNase peptides (17,33). Most importantly, no detectable hemolysis was found at concentrations up to 25 M, and 50% lysis was achieved at 217 Ϯ 42.17 M for the RNase 3 protein and 178,33 Ϯ 81.72 M for the RN3(5-17P22-36) peptide.…”

“…The antimicrobial activity of the secreted human RNases is mainly located at the N-terminal region (17). Accordingly, the RNase antimicrobial scaffold was engineered to produce new antimicrobial peptides (23,33,54).…”

“…AMPs are small, amphipathic, and frequently cationic molecules that present a rapid, high-potency, and broad-spectrum action against microorganisms (14)(15)(16). In our laboratory, we study human RNases as a new potential source of alternative antimicrobial agents (17,18). Human RNase 3, also known as the eosinophil cationic protein (ECP), is a small, highly cationic protein (pI ϳ11) that is stored in the secondary granules of eosinophils (19,20).…”

Defense peptides: recent developments

“…The study conducted by Anantharaman et al (127) showed that a combination of four designed peptides, which had poor to moderate antimicrobial activity, with rifampicin or kanamycin enhanced their potencies against E. coli 4-to 34-fold, respectively. Synergistic effects were reported for the lactoferrin-derived peptide hLF (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and fluconazole against C. albicans. It was also observed that lactoferrin or hLF(1-11) added in subinhibitory concentrations to antifungal agents such as clotrimazole, ketoconazole, and intraconazole reduced the minimum inhibitory concentration of these agents against Candida species (108,128,129).…”

“…In addition, small proteins, e.g. RNase A family members, also exhibit antimicrobial activity, and their involvement in anti-pathogen defense has been well documented (7). Usually, a set of defense peptides differing in biochemical properties and mechanism of antimicrobial action is synthesized by a given organism.…”