RI is also rich in leucine (21.5%, compared to 9% in typical proteins) and commensurately lower in other hydrophobic residues, esp.

RI is the classic leucine-rich repeat protein, consisting of alternating α-helices and β-strands along its backbone.

The structure appears to be stabilized by buried asparagines at the base of each turn, as it passes from α-helix to β-strand.

The affinity of RI for ribonucleases is among the highest for any protein-protein interaction; the dissociation constant of the RI-RNase A complex is in the femtomolar (fM) range under physiological conditions.

In particular, amphibian RNases, such ranpirnase and amphinase from the Northern leopard frog, escape mammalian RI and have been noted to have differential cytotoxicity against cancer cells.