Aspartate residues ribonuclease

Schultz observed (Schultz et al., 1961) that on partial hydrolysis of a commercial preparation of ribonuclease with 0.03 N HCl for times varying up to 48 hr at 105°C, up to 14 out of the 15 bound aspartic residues were liberated. He recommends the method for rapid comparative fingerprinting of the resulting peptides from proteins such as human and animal sera, heme proteins, pepsin, and albumins. 

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. 

In a classic study on bovine pancreatic ribonuclease A at 90°C and pH conditions relevant for catalysis, irreversible deactivation behavior was found to be a function of pH (Zale, 1986) at pH 4, enzyme inactivation is caused mainly by hydrolysis of peptide bonds at aspartic acid residues as well as deamidation of asparagine and/or glutamine residues, whereas at pH 6-8, enzyme inactivation is caused mainly by thiol-disulfide interchange but also by fi-elimination of cystine residues, and deamidation of asparagine and/or glutamine residues. 

Over 50% of the aspartic acid of the proteins of hepatic origin is liberated in 16 hours, but the gamma-globulins of extrahepatic origin required 36 hours to reach 50%. The extent to which this reflects certain characteristics of the primary structure is described in similar studies on insulin, ribonuclease, and glucagon (37). The cleavage of the peptide chain at the aspartic acid bonds may release other amino acids when they are between aspartic acid residues, when the aspartic acid is penultimate at either end of the chain, or if the other residues occupy positions of particularly labile sequences not known at this time. The... 

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. 

Similarly to NEUl, NEU2 contains multiple Asp-box motifs of which one is less conserved (residues 247-254) and two are eanonical Asp-boxes (residues 129-136 and 199-206). Stmcturally, Asp boxes show a (3-hairpin structure stabilized by a water molecule at the center of three eonserved residues of serine, aspartate, and tryptophan, and are found in topologically equivalent positions in all members of the sialidase gene family. Interestingly, Asp-boxes are found in protein families having different sequences and three-dimensional structures, sueh as bacterial ribonucleases, reelin,... 

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