Journal
INORGANIC CHEMISTRY
Volume 56, Issue 1, Pages 313-320Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.6b02189
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Funding
- Research Projects in Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences [Z01-ES043010, Z01-ES050158, Z01-ES050159]
- National Institutes of Health [U19CA105010]
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The transfer of phosphate groups is an essential function of many intracellular biological enzymes. The transfer is in many cases facilitated by a protein scaffold involving two closely spaced magnesium ions. It has long been a mystery how these ions can retain their closely spaced positions throughout enzymatic phosphate transfer: Coulomb's law would dictate large repulsive forces between these ions at the observed distances. Here we show, however, that the electron density can be borrowed from nearby electron-rich oxygens to populate a bonding molecular orbital that is largely localized between the magnesium ions. The result is that the Mg-Mg core of these phosphate transfer enzymes is surprisingly similar to a metastable [Mg-2](2+) ion in the gas phase, an ion that has been identified experimentally and studied with high-level quantum-mechanical calculations. This similarity is confirmed by comparative computations of the electron densities of [Mg-2](2+) in the gas phase and the Mg-Mg core in the structures derived from QM/MM studies of high-resolution X-ray crystal structures. That there is a level of covalent bonding between the two Mg ions at the core of these enzymes is a novel concept that enables an improved vision of how these enzymes function at the molecular level. The concept is broader than magnesium-other biologically relevant metals (e.g., Mn and Zn) can also form similar stabilizing covalent Me-Me bonds in both organometallic and inorganic crystals.
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