Structural and functional studies on the overproduced L11 protein from Thermus thermophilus

The L11 ribosomal protein from Thermus thermophilus (TthL11) has been overp roduced and purified to homogeneity using a two-step purification protocol. The overproduced protein carries a similar methylation pattern at Lys-3 as does its homolog from Escherichia coli. Chymotrypsin digested only a small part of the TthL11 protein and did not cleave TthL11 into two peptides, as in the case of EcoL11, but produced only a single N-terminal peptide. Tryp tic digestion of TthL11 also produced an N-terminal peptide, in contrast to the C-terminal peptide obtained with L11 from Bacillus stearothermophilus. The recombinant protein forms a specific complex with a 55-nt 23S rRNA fra gment known to interact with members of the L11 family from several organis ms. Cooperative binding of TthL11 and thiostrepton to 23S rRNA leads to an increased protection of TthL11 from tryptic digestion. The similar structur al and biochemical properties as well as the significant homology between L 11 from E. coli and B. stearothermophilus with the corresponding protein fr om Thermus thermophilus indicate an evolutionarily conserved protein import ant for ribosome function.