Posttranslational modifications secondary modification

ExPASy Proteomics tools (http //expasy.org/tools/), tools and online programs for protein identification and characterization, similarity searches, pattern and profile searches, posttranslational modification prediction, topology prediction, primary structure analysis, or secondary and tertiary structure prediction. 

Figure 18 Conserved active-site residues in ASs. Numbering is for human ASA. Highlighted are highly conserved residues, underlined residues are involved in metal binding, and in red are the cysteine residues that undergo posttranslational modification to FGIy. The secondary structure DSSP assignment is according to the ASA structure (PDB code 1AUK) ...

The elements of protein structure are divided into four classes primary, secondary, tertiary, and quaternary. Primary structure refers to the linear sequence of amino acids linked by amide bonds along protein chains. These polymer chains vary in length from a few amino acid residues (oligopeptides) to molecules containing 2000 or more amino acids. Most proteins are from 100 to 500 amino acid residues in length. One or more of each of 20 natural amino acids may be present in each protein molecule. In some cases the amino acids undergo posttranslational chemical modification, which introduces still more variety into protein structure. 

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