Structural Biochemistry, Enzyme, Evolution of Enzymes

Evolution is change in the genetic material of a population of organisms from one generation to the next. Evidence of evolution of enzymes have been found by examining multiple enzymes with similar characteristics.

Catalytic Triads

Catalytic triads are found in other hydrolytic enzymes similar to that in chymotrypsin. These sequences of proteins are approximately 40% identical and have nearly the same overall structure. However, these proteins differ in substrate specificity. Other members of this family include a collection of proteins that take part in blood clotting. Other enzymes that are not homologues of chymotrypsin have been found to contain very similar active sites. The presence of very similar active sites in different protein families is a consequence of convergent evolution. Furthermore, other proteases have been discovered that contain an active site serine or threonine residue that is activated by a different side chain. It can be concluded that the catalytic triad in proteases is especially effective in the hydrolysis of peptides because of its frequency of occurrence in different enzymes.

Zinc Based Active Sites

Carbonic anhydrases homologous to the human enzymes are common in animals and some bacteria and algae. In addition, two other families of carbonic anhydrases have been discovered for catalytic activity. In plants, beta carbonic anhydrases are found and revealed that although it has a bound zinc ion similar to alpha carbonic anhydrases the structures are unrelated. Gamma carbonic anhydrases were discovered to have three zinc sites similar to the alpha carbonic anhydrases. Convergent evolution has generated carbonic anhydrases that rely on coordinated zinc ions at least three times.

P-Loop Domains

Domains similar in NMP kinases are present in a wide array of proteins. Examples include ATP synthase, molecular motor proteins, signal transduction, and translation. The wide utility of P-loop NTPase domains is perhaps best explained by their ability to undergo substantial conformational changes.

References

Berg, Jeremy M. John L. Tymoczko. Lubert Stryer. Biochemistry Sixth Edition. W.H. Freeman and Company. New York, 2007.

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