Structural bases of hexacoordination in globins

BORÓN, I., CAPECE, L., PENNACCHIETTI, F., WETZLER, D., BRUNO, S., CHISARI, L., ABBRUZZETTI, S., LUQUE, J., VIAPPIANI, C., MARTÍ, M, ESTRÍN, D., AND NADRA, AD.

Puerto Varas

Congreso; IV Latin American Protein Society Meeting; 2013

Latin American Protein Society

Mb is one of the most studied proteins. Its physiological function and the availability of its structure several decades ago helped to conceive Mb as the reference protein to develop and test many biophysical techniques. Mb was also the subject of many mutational studies, rational protein design and complete sequence re-writing. Mb provided the traditional picture of a globin: globular, heme coordinating, pentacoordinated, O2 binder protein. In the last decade, however, several hexacoordinated globin were discovered and a role for hexacoordination in protein function was proposed. Among them, there is a particular interest in Neuroglobin (Ngb), which is expressed in the nervous system of vertebrates. In previous studies we established that the CD region in Ngb is involved in the 5c-6c equilibrium. Aiming to shed light on the key determinants for globin hexacoordination, in this work we engineered Mb and Ngb by swapping their CD region willing to exchange protein behavior. We have computationally and experimentally characterized different coordination and oxidation states for chimeric Mb and chimeric Ngb. Equilibrium and kinetic spectroscopy, hexacoordination free energy profiles and ligand binding for both proteins showed that swapped CD region favors Mb hexacoordination as well as Ngb pentacoordination in physiological conditions.