Variable Temperature Resonance Raman Spectroscopic Studies of MauG

Faculty #14
Discipline: Chemistry and Chemical Sciences
Subcategory: STEM Research

Manliang Feng - Tougaloo College
Co-Author(s): Breland Crudup and Contesa Franklin, Tougaloo College, Tougaloo, MS

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MauG is a di-heme protein that catalyzes the posttranslational modification the two endogenous tryptophan residues at the active site of precursor methylamine dehydrogenase (Pre-MADH). It shares sequence and structural homology with di-heme cytochrome c peroxidase (CcP) but the biological role and reaction mechanisms are quite different. Previous X-ray crystallographic , EPR, resonance Raman (RR) and UV-Vis spectroscopic results indicate that the two hemes in MauG are different in coordination and spin states. One heme is pentacoordinated with His35 as the proximal ligand. The other heme is hexacoordinated with His205 and Tyr294 as the proximal and distal ligand. The penta-coordinated high-spin heme is believed to directly react with oxygen donating substrates (H2O2 or O2) to allow the protein to form a bis-Fe(IV) species through charge-resonance among the two hemes and an intervening tryptophan residue. In this study, RR spectra of MauG were studied at various temperatures (77K, 202K, 232K and 293K) and a temperature dependent structural changes at high spin heme site was observed. At lower temperature, the high spin heme is mainly 5-coordinated while at higher temperature it appears as a mixture of penta/hexa coordinated high-spin heme. The ratio of the 6- to 5- coordinated heme increases with raising temperature. This result implies an equilibrium between the two conformational sub-states (conformers) of MauG, which may play a role in the charge-resonance and fast long range electron transfer of the protein. RR and Fourier Transformed Infrared (FTIR) spectra of ferrous MauG-CO adduct indicate that the two forms of MauG have discrete conformations as evidence by the 2 vC=O bands. The vFe-CO and vC=O correlations of the two forms point to a conclusion that the proximal linkages of the high-spin heme in one of MauG conformer is stronger than a normal heme with a histidine proximal ligand.

Funder Acknowledgement(s): This work is supported by NSF Research Initiation Award under HBCU-UP program (Award number: 1505446).

Faculty Advisor: None Listed,