L22 ribosomal protein and effect of its mutation on ribosome resistance to erythromycin

The ribosomal protein L22 is a core protein of the large ribosomal subunit interacting with all domains of the 23 S rRNA. The triplet Met82-Lys83-Arg84 deletion in L22 from Escherichia coli renders cells resistant to erythromycin which is known as an inhibitor of the nascent peptide chain elongation. The crystal structure of the Thermus thermophilus L22 mutant with equivalent triplet Leu82-Lys83-Arg84 deletion has been determined at 1.8 Angstrom resolution. The superpositions of the mutant and the wild-type L22 structures within the 50 S subunits from Haloarcula marismortui and Deinococcus radiodurans show that 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 P-hairpin. The mutation in the L22 P-hairpin affects the orientation and distances between those nucleotides. This destabilizes 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. (C) 2002 Elsevier Science Ltd. All rights reserved.