The mechanism of the transpersulfuration reaction in a cysteine desulfurase-sulfur acceptor model system

Trabajo presentado en las 1as Jornadas Españolas de Biocatálisis, celebradas en Madrid (España) del 02 al 03 de julio de 2015.Escherichia coli CsdA cysteine desulfurase (the sulfur donor) and the CsdE sulfur acceptor are involved in biological sulfur trafficking, in iron-sulfur cluster assembly, and tRNA hypermodification [1] in the model bacterium Escherichia coli. CsdA and CsdE form a stable complex through a polar interface. Although mechanisms for the transfer of a sulfur moiety across protein-protein interfaces have been proposed based on the IscS-IscU and IscS-TusA structures [2,3], the flexibility of the catalytic Cys loops involved has precluded a high resolution view of the active-site geometry and chemical environment responsible to facilitate sulfur transfer. Here, we have used a combination of X-ray crystallography, solution NMR, biophysical and computational chemistry methods to unravel how CsdA provides a specific recognition platform for CsdE and how their complex organizes a composite functional reaction environment. A mechanistic view of sulfur transfer across protein-protein interfaces emerges from the structural analysis of the CSD system