The protease thermolysin contains a Zn+2 metal ion that plays a critical role in its enzymatic activity. The zinc ion is held in the proper position in the protein by close interaction with three amino acid side chains: H69, E72, and H196. (i) Explain how three amino acids that are not immediately adjacent to each other in the sequence can still occupy points in space that are within a few angstroms of each other. (ii) Histidine is the amino acid most commonly found at catalytic active sites. Why?
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Proteins fold into complex shapes, and the linear sequence of amino acids in the primary structure (the sequence of the protein) folds into a specific three-dimensional structure known as the tertiary structure. This folding allows amino acids that are far apart Show more…
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The image below shows the structure of an enzyme in its tertiary form. Its active site contains Histidine and Aspartate residues that are essential for catalytic function. Answer the two questions below. a) Describe the forces that stabilise each secondary structure in this enzyme, as well as the types of residues that would make up the internal core of the protein. b) The codon that codes for the Histidine in the active site has undergone a mutation and now codes for a Tyrosine residue instead. Describe what type of catalytic role the Histidine and Aspartate residue normally play, and describe how the substitution of the Histidine for the Tyrosine residue would alter the enzyme's catalytic function.
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