Direct NMR observation of the Cys-14 thiol proton of reduced Escherichia coli glutaredoxin-3 supports the presence of an active site thiol-thiolate hydrogen bond. |
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Authors: | K Nordstrand F Aslund S Meunier A Holmgren G Otting K D Berndt |
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Affiliation: | Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden. |
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Abstract: | The active site of Escherichia coli glutaredoxin-3 (Grx3) consists of two redox active cysteine residues in the sequence -C11-P-Y-C14-H-. The 1H NMR resonance of the cysteine thiol proton of Cys-14 in reduced Grx3 is observed at 7.6 ppm. The large downfield shift and NOEs observed with this thiol proton resonance suggest the presence of a hydrogen bond with the Cys-11 thiolate, which is shown to have an abnormally low pKa value. A hydrogen bond would also agree with activity data of Grx3 active site mutants. Furthermore, the activity is reduced in a Grx3 H15V mutant, indicating electrostatic contributions to the stabilization of the Cys-11 thiolate. |
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