Glutamate residues ribonuclease

Mizrahi V, Brooksbank RL, Nkabinde NC. Mutagenesis of the conserved aspartic acid 443, glutamic acid 478, asparagine 494, and aspartic acid 498 residues in the ribonuclease H domain of p66/p51 human immunodeficiency vims type 1 reverse transcriptase. JBiol Chem 1994 269 19245-19249. 

Bovine pancreatic RNase A is a member of a homologous superfamily. In addition, there is a separate family of guanine-specific microbial RNases that have evolved to have a similar active site.192,193 Ribonuclease T1 from Aspergillus oryzae and the 110-residue bamase from Bacillus amyloliquefaciens of Mr 12 392 (see Chapter 19) are the best known examples. One of the histidine residues is replaced by a glutamate in these enzymes. The microbial enzymes are much more amenable to study by protein engineering. 

Figure 21 shows the previously published sequence of residues 11-18 of ribonuclease (Hirs, et al, I960). Previous studies (Redfield and Anfinsen, 1956 Anfinsen et al, 1956) have suggested that residue 11 is glutamic acid rather than serine. The results with cyanogen bromide cleavage discussed above are consistent with the latter assignment for position 11. Thus cleav-... 

Later, other workers confirmed these findings which are summarized in Table 2. Thus isopeptides to date have been found to be formed during heating in keratin (40), milk proteins (41), muscle proteins (42), ribonuclease (4 )" and other proteins of nutritional interest (44). The ease of formation of the isopeptide in any specific protein should be dependent on two factors firstly, the concentration of glutamic and aspartic acids in relation to the concentration of lysine and, secondly, the proximity of the lysyl and carboxylic residues which will be determined by the conformation of the protein chain. 

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