Meeting Abstract
31.4 Sunday, Jan. 5 08:45 Evolution takes baby steps: The mutational trajectory of the emergence of red fluorescence in coral fluorescent proteins MODI, C.K.*; CHANDLER, C.; MATZ, M.V.; The University of Texas at Austin; University of Michigan; The University of Texas at Austin Chintan.Modi@utexas.edu
Epistatically interacting amino acids are hypothesized to be instrumental in the evolution of the structure-function relationship of many proteins. Our previous analysis of resurrected ancestral proteins identified 12 epistatically interacting historical mutations associated with the evolution of the complex autocatalytic pathway leading to red fluorescence in coral fluorescent proteins (FPs). How have such extensive combinations been assembled through natural selection? The goal of the present study was to determine the minimal set of historical mutations that led to the first appearance of detectable red fluorescence from the ancestral green state. By examining the effects of individual mutations and their combinations in the green-fluorescent ancestral FP we found that just three point mutations are sufficient to initiate red fluorescence evolution: one in the chromophore-forming tripeptide, another in its immediate vicinity, and the third in a cluster of C-terminal residues, reducing the protein’s oligomerization tendency. Notably, two of these three mutations had a significant destabilizing effect on the protein, as evidenced by its reduced thermostability. Comparison of the mutants with the ancestral and extant FPs (a vertical phylogenetically based comparative method) allowed detection of the small effects of epistatically interacting residues on the initial evolutionary trajectories toward increased molecular complexity and novel molecular function. Our observations support the theory that evolution of even the most complex epistatic interactions could be initiated by few and therefore relatively probable mutations, and also highlights the need for destabilization of the ancestral structure to enable the evolution of novelty.
