Metalloprotein entatic control of ligand-metal bonds quantified by ultrafast x-ray spectroscopy

• Autores: Michael W. Mara, Ryan G. Hadt, Marco Eli Reinhard
• Localización: Science, ISSN 0036-8075, Vol. 356, Nº 6344, 2017, págs. 1276-1280
• Idioma: inglés
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• Resumen

  • The multifunctional protein cytochrome c (cyt c) plays key roles in electron transport and apoptosis, switching function by modulating bonding between a heme iron and the sulfur in a methionine residue. This Fe–S(Met) bond is too weak to persist in the absence of protein constraints. We ruptured the bond in ferrous cyt c using an optical laser pulse and monitored the bond reformation within the protein active site using ultrafast x-ray pulses from an x-ray free-electron laser, determining that the Fe–S(Met) bond enthalpy is ~4 kcal/mol stronger than in the absence of protein constraints. The 4 kcal/mol is comparable with calculations of stabilization effects in other systems, demonstrating how biological systems use an entatic state for modest yet accessible energetics to modulate chemical function.