E. coli ribosomal protein

In recent years a number of in vitro studies have shown that the presence of Met(O) residues in a wide variety of proteins causes loss of biological activity. Table 2 lists some proteins which have been demonstrated to lose activity when specific Met residues are oxidized in vitro. Two of these proteins, E. coli ribosomal protein LI 2 and mammalian a-1-PI, have been studied extensively and will be discussed in detail. 

Three major methods have been employed for the isolation of all E. coli ribosomal proteins. 

Most of the E. coli ribosomal proteins are rather basic with high isoelectric points (Kaltschmidt, 1971) and a high content of basic amino acids (Tables I and II). The complete primary structures of all . coli ribosomal proteins have been determined by Wittmann-Liebold and coworkers (see Table III and Appendix). 

Occurrence of Modified Amino Acids in E. coli Ribosomal Proteins"... 

The existence of flexible regions in ribosomal proteins can be explored by studying the action of proteolytic enzymes under mild conditions. It has been found that many E. coli ribosomal proteins consist of two domains one compactly folded and resistant to proteolysis, the other flexible and vulnerable to proteases (Littlechild et al, 1983). Some proteins (S15, S16, S17, and L30) are very resistant whereas others (S2, S6, S9, L2, L27, L29, and L33) are completely degraded without the appearance of discrete fragments. The remaining proteins yield fragments of various size under these conditions. 

The only other E. coli ribosomal protein whose crystallization has so far been reported is L29 (Appelt et al., 1981). On the other hand, attempts to crystallize ribosomal proteins from the thermophilic Bacillus stearothermophilus have been more successful. Protein BL17, which according to its amino acid sequence (Kimura et al., 1980) corresponds to protein L9 from the E. coli ribosome (Kimura et al., 1982), was the first intact ribosomal protein to give crystals useful for X-ray structural analysis (Appelt et al., 1979). Several other B. stearothermophUus ribosomal proteins, namely BL6 and BL30 (Appelt eteU., 1981,1983) from the large and BS5 (Appelt et al., 1983) from the small subunit have been crystallized, and the determination of their three-dimensional structure at a resolution of better than 3 A is now in progress. Furthermore, crystals of aB. stearothermophilus ribosomal protein complex, which corresponds to the complex (L7/L12)4 LIO from E. coli ribosome, have been obtained (Liljas and Newcomer, 1981). 

The proteins of the 30S subunit are termed S1,S2,...,S21 (in this context, S is for small subunit) one copy of each is contained in the 30S subunit. The proteins of the 50S subunit are denoted by L (for large subunit). Each 508 subunit contains one copy of each protein molecule, except for proteins L7 and LI2, of which there are four copies, and L26, which is not considered to be a true component of the 508 subunit. Most ribosomal proteins are very basic proteins, containing up to 34% basic amino acids. This basicity probably accounts in part for their strong association with the RNA, which is acidic. The amino acid sequences of most of the E. coli ribosomal proteins are known. A summary of the structure of the E. coli 708 ribosome is shown in Figure 25-10. 

As mentioned above, it was concluded from immunological studies that there is no extensive homology among E. coli ribosomal proteins, and this has also been confirmed by the amino acid sequence analyses which have so far been performed. With the exception of the two pairs of proteins described above, only very short regions of homology (up to five residues) occur. This finding is based on the sequence determination of about 3000 amino acid residues, i.e. 35 % of the approximately 8000 amino acids present in the E. coli ribosome. 

The knowledge of the primary structures which can be expected for most E. coli ribosomal proteins within the not too far distant future is an essential prerequisite for a number of further objectives (a) an understanding at the molecular level of the specific recognition and interaction between ribosomal RNA and proteins (b) the determination of the spatial structure of ribosomal proteins which is now in its very early stage (c) the elucidation of amino acid replacements and more drastic differences in ribosomal proteins from mutants with altered phenotypes, e.g. resistance to or dependence on antibiotics (d) a comparison of the structure of ribosomal proteins from organisms belonging to different bacteria, plants or animals with a view to obtaining information about the evolution of ribosomes. 

Specific ribosomal components have an important function in relation to the fidelity of protein synthesis. Thus, in E. coli ribosomal protein S12 determines the accuracy of codon-anticodon interactions and modulates the... 

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