Discipline: Chemistry & Chemical Sciences
Subcategory: STEM Research
- Tougaloo College
Co-Author(s): Jamease Williams and John Johnson, Tougaloo College, Tougaloo MS; Yiming Liu, Jackson State University, Jackson MS
The diheme enzyme MauG catalyzes oxidative post-translational modifications of a protein substrate, precursor protein of methylamine dehydrogenase (preMADH), which consists of a native tryptophan residue (βTrp108) and a 7-hydroxylated tryptophan (βTrp57). The reaction results in the covalent crosslinking of βTrp57 to βTrp108, insertion of a second oxygen atom into the side-chain of βTrp57, and oxidation of the quinol species to the quinone. Despite extensive works on the mechanism of the MADH maturation reaction it is still unclear how the βTrp57 gain the first hydroxyl group forming the preMADH. In this research, we have found that tryptophan could gain the first hydroxyl group via reacting with hydrogen peroxide. MauG catalyzes the oxidation reaction and the subsequent cross-linking reaction. The kinetic of the reaction was studied using UV-Visible absorption spectroscopy and supported by LC-MS spectroscopy. Analysis of the kinetic data indicates MauG catalyzes the insertion of first oxygen to tryptophan with a rate constant of 2.8 × 10-3. The LC-MS study of the reaction indicates that tryptophan is first converted to a mono hydroxyl tryptophan which is then quickly converted to a di-hydroxy tryptophan. The reaction then proceeds to form cross-linked tryptophan which is evidence by a dimer peak in LC-MS and small increase of absorbance at 350 nm. Comparing the enzyme catalyzed reaction with the non-catalyzed oxidation reaction, it is found that the oxygen insertion can take place without MauG but with a much slower rate. The cross-linking reaction is MauG specific. . This study may help to fully understand the biosynthesis of MADH through post-translational modification.
Funder Acknowledgement(s): This work is supported by NSF Research Initiation Award under HBCU-UP program (Award number: 505446)
Faculty Advisor: None Listed,