The conformation of biliverdin in dimethyl sulfoxide: implications for the coordination with copper
Biliverdin (BV) structure was analyzed by using NMR techniques and unrestricted density function theory simulations to explain the incapacity of BV to build coordination complex(es) with Cu2+ in dimethyl sulfoxide, which was confirmed by UV-Vis, EPR and NMR spectroscopy. NMR showed that N atoms are protonated in all four pyrrole rings. The structure is stabilized by two hydrogen bonds between NH moieties and carbonyl oxygens from opposite terminal pyrrole rings, and by the bending of propionyl chain with carboxyl group out of the plain toward central position of BV. The simulations of deprotonated BV, which builds copper complexes in water and chloroform as described previously, showed a different conformation and organization of hydrogen bonds. Taking into account that deprotonation represents a critical step in coordinate bonds formation, the protonation of an additional N atom may represent a key difference between the interactions of BV with copper in different solvents.
KeywordsBiliverdin Copper Hydrogen bonds NOESY UDFT
We are thankful to Prof. Miloš Mojović at EPR Laboratory, Faculty of Physical Chemistry, University of Belgrade for recording EPR spectra and to Ljiljana Stojanović from School of Biological and Chemical Sciences, Queen Mary University of London, for her great help in calculating and discussing theoretical results obtained using the UDFT.
This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (III43010). This article is based upon work from COST Action CA15133 FesBioNet, supported by COST (European Cooperation in Science and Technology).
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Conflict of interest
The authors declare that they have no conflict of interest.
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