MreB

Source: The Journal of Cell Biology

Why?

Prior to the advent of x-ray crystallography, one of the defining characteristics of prokaryotes was “lacks a cytoskeleton.” However, when the crystal structure of bacterial MreB was found, scientists discovered that MreB and eukaryotic actin “look” nearly identical. It turned that notion completely upside down, rewriting textbooks, and scientists have been studying these homologs – and the evolutionary origins of these proteins – ever since. —Kelly Tyrrell