This superfamily entry represents the ribosomal protein L22 found in the large 50S subunit of the ribosome in bacteria, mitochondria and chloroplast. The eukaryotic homologue of L22 is L17. The molecule is a whole-chain domain with an alpha/beta fold, and consists of three alpha-helices packed against a three-stranded antiparallel beta-sheet. The alpha-helices and beta-sheet form a compact, globular domain, a well-packed hydrophobic core without charged or polar residues. A beta-hairpin enriched with hydrophobic residues is formed by strands beta-2 and beta-3 and protrudes from the core of the protein.

L22 is the largest protein contributor to the surface of the polypeptide exit channel, the tunnel through which the polypeptide product passes. It is the only ribosomal protein that interacts with all six domains of 23S rRNA, and is one of the proteins important for directing the proper folding and stabilising the conformation of 23S rRNA. L22 is also one of six proteins located at the putative translocon binding site on the exterior surface of the ribosome. The nascent polypeptide interacts with the beta-hairpin of L22.

The triplet Met82-Lys83-Arg84 deletion in L22 from Escherichia coli gives rise to resistance to erythromycin, an inhibitor of the nascent peptide chain elongation. The mutant beta-hairpin is bent inward the ribosome tunnel modifying the shape of its narrowest part and affecting the interaction between L22 and 23 S rRNA. 23 S rRNA nucleotides of domain V participating in erythromycin binding are located on the opposite sides of the tunnel and are brought to those positions by the interaction of the 23 S rRNA with the L22 beta-hairpin. The mutation in the L22 beta-hairpin affects the orientation and distances between those nucleotides. This destabilises the erythromycin-binding "pocket" formed by 23 S rRNA nucleotides exposed at the tunnel surface. It seems that erythromycin, while still being able to interact with one side of the tunnel but not reaching the other, is therefore unable to block the polypeptide growth in the drug-resistant ribosome.

PFAM:PF00237, INTERPRO:IPR036394,PMID:12225755,PMID:25278503,PMID:9862810