Ribonuclease inhibitor
| Leucine Rich Repeat | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Top view of porcine ribonuclease inhibitor, showing its horseshoe shape. The outer layer is composed of α-helices and the inner layer of parallel β-strands. The inner and outer diameters are roughly 2.1 nm and 6.7 nm, respectively. | |||||||||||
| Identifiers | |||||||||||
| Symbol | LRR_1 | ||||||||||
| Pfam | PF00560 | ||||||||||
| Pfam clan | CL0022 | ||||||||||
| InterPro | IPR003590 | ||||||||||
| SMART | SM00368 | ||||||||||
| SCOP2 | 1bnh / SCOPe / SUPFAM | ||||||||||
| |||||||||||
Ribonuclease inhibitor (RI) is a large (~450 residues, ~49 kDa), acidic (pI ~4.7), leucine-rich repeat protein that forms extremely tight complexes with certain ribonucleases. It is a major cellular protein, comprising ~0.1% of all cellular protein by weight, and appears to play an important role in regulating the lifetime of RNA.
RI has a surprisingly high cysteine content (~6.5%, cf. 1.7% in typical proteins) and is sensitive to oxidation. RI is also rich in leucine (21.5%, compared to 9% in typical proteins) and commensurately lower in other hydrophobic residues, esp. valine, isoleucine, methionine, tyrosine, and phenylalanine.