Two human host defense ribonucleases against mycobacteria, the eosinophil cationic protein (RNase 3) and RNase 7.

There is an urgent need to develop new agents against mycobacterial infections, such as tuberculosis and other respiratory tract or skin affections. In this study, we have tested two human antimicrobial RNases against mycobacteria. RNase 3, also called the eosinophil cationic protein, and RNase 7 are two small cationic proteins secreted by innate cells during host defense. Both proteins are induced upon infection displaying a wide range of antipathogen activities. In particular, they are released by leukocytes and epithelial cells, contributing to tissue protection. Here, the two RNases have been proven effective against Mycobacterium vaccae at a low micromolar level. High bactericidal activity correlated with their bacterial membrane depolarization and permeabilization activities. Further analysis on both protein-derived peptides identified for RNase 3 an N-terminus fragment that is even more active than the parental protein. Also, a potent bacterial agglutinating activity was unique to RNase 3 and its derived peptide. The particular biophysical properties of the RNase 3 active peptide are envisaged as a suitable reference for the development of novel antimycobacterial drugs. The results support the contribution of secreted RNases to the host immune response against mycobacteria.

Dynamics of the native and the ligand-bound structures of eosinophil cationic protein: network of hydrogen bonds at the catalytic site.

Eosinophil Cationic Protein (ECP) is sequentially and structurally similar to ribonuclease A (RNase A). It belongs to the RNase A family of proteins and the RNA catalysis is essential to its biological function. In the present study, we have generated the dinucleotide-bound structures of ECP by docking the dinucleotides to a number of molecular dynamics (MD) generated ECP structures. The stability of the docked enzyme-ligand complexes was ascertained by extensive MD simulations. The modes of ligand binding are explored by essential dynamics studies. The role of water molecules in the stability of the complex and in the catalysis was investigated. The active site residues form a complex network of connections with the ligand and with a water molecule. The catalytic mechanism of the RNA cleavage is examined on the basis of the active site geometry obtained by the simulations.