In a recent Biochemistry paper, the Martin lab reports the biophysical characterization of a highly stable Ca2+ binding protein from the tunicate Ciona intestinalis. The tunicate is a chordate related to the ancestors of all vertebrates, and investigation of its crystallin protein provides insight into the evolution of the structural proteins making up the vertebrate eye lens. The tunicate crystallin binds Ca2+ with high affinity, and Ca2+ dramatically stabilizes the protein’s thermal and chemical stability, enabling it to remain folded at 90 °C and in the presence of 8.5 M urea! These results provide a basis for understanding the evolution of human crystallins, in particular how crystallins made the transition from their ancestral function as Ca2+-binding proteins to making up the primary refractive medium of the human lens.
Natalia Kozlyuk, Suvrajit Sengupta, Jan Bierma, and Rachel W. Martin