Ribonuclease inhibitor (RI)

Ribonuclease inhibitor is a large (≈50 kDa), acidic, leucine-rich repeat (LRR) cytosolic protein found at high concentrations throughout mammalian tissues. RI forms exceptionally tight complexes (femtomolar affinity) with members of the pancreatic ribonuclease superfamily, notably RNase A and angiogenin, and effectively inhibits their activity. Structurally, RI is horseshoe-shaped with alternating α-helices and β-strands, stabilized by conserved leucine and cysteine residues. Biologically, RI protects cellular RNA by neutralizing ribonuclease activity and maintaining redox homeostasis, as its function depends on a reduced thiol state. RI plays roles in embryonic development, oxidative stress resistance, RNA metabolism, and potentially angiogenesis, although the full physiological importance in humans remains incompletely understood[1][2][3][5][6].\n\n**Note:** The molecule is not a classical receptor, enzyme, transporter, or drug target, but is highly significant in protein-protein interaction networks and molecular biology research.

Other names

RNase inhibitorRNH1 (Angiogenin inhibitor 1)ribonuclease inhibitor (RI)leucine-rich repeat proteinangiogenin inhibitor 1

Not applicable for drugs targeting RI; for interacting ribonucleases (e.g., ranpirnase, angiogenin), the mechanism involves escaping RI-dependent inhibition, allowing ribonuclease-induced RNA degradation and possible cytotoxicity