Multifunctional enzymes and evolution of biosynthetic pathways: retro-evolution by jumps.
A likely scenario of evolution of biosynthetic pathways is believed to have occurred by retro-evolution through recruitment of existing enzymes rather than generation of de novo classes. It had been proposed that such retro-evolution occurred in steps as a response to depletion of an essential metabolite and availability of another related substance in the environment. In this article, I argue that because of instability of many such extant intermediates, it is unlikely that retro-evolution had occurred in steps. I further propose that such evolution in many cases has taken place by jumps, i.e., by recruitment of a multifunctional enzyme capable of catalyzing several steps at a time, albeit inefficiently. I further speculate that in some cases one primordial multienzyme may have catalyzed the whole sequence of reaction of a biosynthetic pathway, i.e., the pathway may have evolved by a single leap. Gene duplications and further evolution to more efficient enzymes led to extant pathways. Such a mechanism predicts that some or all enzymes of a pathway must have descended from a common ancestor. Sequence and structural homologies among extant enzymes of a biosynthetic pathway have been examined.
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Department of Biophysics, Bose Institute, Calcutta, India. siddarth@boseinst.ernet.in
D000596:Amino Acids / Q000096:biosynthesis; D001419:Bacteria / Q000201:enzymology / Q000378:metabolism; D002384:Catalysis; D003960:Diaminopimelic Acid / Q000378:metabolism; D004798:Enzymes / Q000096:biosynthesis* / Q000737:chemistry; D019143:Evolution, Molecular; D008715:Methionine / Q000096:biosynthesis; D008954:Models, Biological; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D011687:Purines / Q000096:biosynthesis
D000596:Amino Acids; D004798:Enzymes; D011687:Purines; D003960:Diaminopimelic Acid; D008715:Methionine; C030985:purine