Serine residues ribonuclease

Serine Proteases Enzymes that Use a Serine Residue for Nucleophilic Catalysis Ribonuclease A An Example of Concerted Acid-Base Catalysis... 

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-... 

This was first foimd by Sanger et al. (1955) in a peptide from insulin and was observed with other peptides by Hirs et al. (1956) and Smyth et al. (1962). The reaction appears to occur when acidic buffers or dilute acids are employed for isolation of peptides. Conversion of the cyclic pyrrolidone carboxyl residue to a glutamyl residue is obtained on mild hydrolysis in dilute acids or alkalies. The cyclization reaction leads to difficulties when sequence methods are used which proceed from the amino-terminal end of a peptide. In addition, this reaction can occur when an internal glutamine residue becomes amino-terminal in the course of stepwise sequence analysis under acidic conditions, as in the Edman methods. An incorrect sequence for a peptide from ribonuclease was deduced as the result of cyclization of amino-terminal glutamine and acidic destruction of serine and threonine in the same peptide (Smyth et al., 1962). 

Several studies with ribonuclease suggest that ( ertain peptide bonds of a given kind are more available to proteolysis than others (reviewed by Scheraga and Rupley, 1962). Thus, pepsin hydrolyzes one bond between residues 120 and 121 which leads to inactivation of the molecule (Anfinsen, 19.56). Subtilisin (Richards and Vithayathil, 1959) rapidly splits a single bond between alanine and serine at residues 20 and 21. Carboxypeptidase... 

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,... 

Further examples of conformational adaptationf will be given, each one quite individual in its mechanism, yet collectively supplying a picture of considerable uniformity. Ribonuclease forms a compact structure, hydrophilic outside, lipophilic inside, with a slot to receive the substrate. The active site makes use of histidine residues (numbers 12 and 119) that would otherwise be remote from one another (Kartha, Bello and Marker, 1967). The dimensions of the folded ribonuclease molecule are about 30X 30X 38 A (mol. wt. 15 000). When charged with a substrate, e.g. cytidine phosphate, one histidine residue binds the phosphate group, the other the sugar. The tertiary structure of a-chymotrypsin has been similarly worked out the active site depends on the closeness of two amino acids that are on different strands, namely serine-195 and histidine-57... 

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