Charles Darwin’s very popular theory of evolution emerged from his observation of chaffinches on the Galapagos Islands. He had recorded 14 different species, from as many different islands, when it became clear to him that, despite differences, the species were nevertheless related. The obvious disparity lay in the shape of their beaks and this was directly related to a specific diet. Chaffinches which lived on flowers and cactus fruit had long narrow beaks, while those which lived off strong-shelled grains had large, powerful beaks. What was it that could drive such differences ? It took the best part of two centuries before anyone could give an answer. And we know today, that the shape of a chaffinch’s beak is dependent on the expression of a protein: calmodulin.
Calmodulin is a small protein, found in every cell from plants to animals. It has also changed very little over time, so much so that human and hen calmoldulins are identical! It must do something very important if it has stayed much the same over the millennia. Indeed, calmodulin is able to perceive changes in the concentration of intracellular calcium and then transmit this crucial information to other proteins. How?
When the level of calcium increases inside a cell, calmodulin binds to four ions, which changes its three-dimensional structure. Initially cramped, calmodulin opens out into two arm-like conformations that can grasp onto other proteins. Consequently, the two ‘grasped’ proteins spring to life and perform their various activities: muscle contraction, the transmission of a nerve signal, the excretion of insulin into the blood system…or the control of craniofacial development such as the chaffinch’s beak!