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., NADRA, AD

Puerto Varas

Congreso; XII Meeting of Pan American Biochemistry & Molecular Biology Societies together with the XLIX Annual Meeting of the Argentinean Society of Biochemistry and Molecular Biology (SAIB) and the 4th Meeting of the Latin-American Protein Society; 2013

P { margin-bottom: 0.08in; TD P { font-family: "Arial",sans-serif; font-size: 9pt; text-align: justify; } 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 iron atom leads to the formation of a hexacoordinated (6c) globin, as noted in neuroglobin (Ngb) and cytoglobin, among others. Ngb, which is expressed in vertebrates nervous system, has been the subject of many investigations in the last years, but its function is still unclear. In our previous work, we have studied by computer simulation the 5c↔6c transition in wild type Ngb, and analyzed the main differences between this protein and Mb, observing that the flexibility of the CD region is a key factor in the hexacoordination process. In this work, by mean of a theoretical-experimental approach, we have studied comparatively Ngb and Mb structure and dynamics as well as those of chimeric proteins exchanging their CD region. Herein we present results of classical molecular dynamics, free energy profiles for the 5c↔6c process, UV-VIS spectroscopy and Stopped Flow and Flash Photolysis analysis. Results suggest that each chimeric protein shifted its coordination state according to its CD region, as shown for the partially hexacoordinated myoglobin or the subtly pentacoordinated Ngb.