A protein that catalyzes one reaction can theoretically be modified by mutations and natural selection and eventually catalyze another reaction completely unrelated to the original. Has this been observed, documented, or at least postulated to be where a certain protein(s) came from?
From the following free review:
Here we review some of the successful strategies in creating protein diversity and the more recent progress in directed protein evolution in a wide range of scientific disciplines and its impacts in chemical, pharmaceutical, and agricultural sciences.
Quoting three examples, but the article has much more:
Directed evolution has been successfully applied to DNA polymerase for enhanced activity (233) and conversion to an efficient RNA polymerase (232, 333).
Naumann and Reznikoff (216) used directed evolution to generate a mutated Tn5 bacterial transposase that could function on transposons with mutated end binding sequences.
Organophosphate-degrading enzymes have been evolved and selected for broadened substrate specificity (53, 335). Broadened substrate specificity of a biphenyl dioxygenase has also been achieved (33, 87, 164, 291). Efforts in cleaning underground water contamination prompted the evolution of an enzyme for chlorinated ethene degradation (41).
L. Yuan, I. Kurek et al: Laboratory-directed protein evolution. In: Microbiology and molecular biology reviews : MMBR. 69, 3, September 2005, 373–392. doi:10.1128/MMBR.69.3.373-392.2005. PMID 16148303. PMC 1197809.