Tinkering with coordination in globins

CHISARI, L., BORON, I., WETZLER, D., CAPECE, L, MARTI, M, ESTRIN, D, NADRA, A

Cordoba

Congreso; XLII Reunión anual de la Sociedad Argentina de Biofísica; 2013

Sociedad Argentina de Biofísica

Background. Human Myoglobin (Mb) and hemoglobin are relevant examples of pentacoordinated (5c) heme proteins and many of their biological functions involve the coordination of exogenous ligands in the sixth position of the heme group. On the other hand, in several globins direct coordination of HisE7 to the Fe atom leads to the formation of a hexacoordinated (6c) globin, as noted in neuroglobin (Ngb) and cytoglobin, among others. It has been suggested that this bond and the equilibrium between the 6c and the 5c state regulate ligand affinity and provide the protein with major thermal stability. Recent work by Nadra et al. has sheded light on the key determinants for globin hexacoordination, engineering Mb and Ngb by swapping their CD region. A partially 6c myoglobin and a subtly 5c Ngb shown that each chimeric protein shifted its coordination state according to its CD region. Goal. With the aim of further displacing the coordination equilibrium, we designed point mutations to enhance the observed behaviour. Results. By exploring the contacts stabilizing the CD region we have found a contact between a lysine and a glutamic acid which may account for Mb's preference for the 5c state. Molecular dynamics simulations, equilibrium spectroscopy and ligand binding results for a chimeric Ngb punctual mutant suggest differences in agreement with the theoretical predictions.