Roseobacter Ruegeria pomeroyi expresses a cupin containing lyase responsible for dimethylsulfoniopropionate (DMSP) catabolism, liberating the climatically active dimethylsulfide (DMS). Approximately 50 million tons of this biogenic volatile sulfur gas is released to the atmosphere annually. R. pomeroyi uses DMSP as a sole carbon and sulfur source, and DMSP lyases cleave DMSP releasing DMS. The enzyme is a member of a less characterized class of DMSP lyases and shares some sequence similarity with other DMSP lyases. Despite the environmental significance of DMS, the mechanism by which these lyases produce DMS is understudied primarily due to the lack of sufficient biochemical and structural data. Sequence analysis suggests that the DMSP-lyase contains conserved cupin residues that bind metal ions and contribute to the enzymatic activity. The metal-binding properties of the DMSP-lyase, DddW, expressed in E. coli were investigated. Measurements of metal binding affinity and catalytic activity indicate that while Fe(II) is the most tightly bound metal ion, both Fe(II) and Mn(II) are preferred catalytic metal ions. Stoichiometry studies suggest the DMSP-lyase requires one metallocofactor per monomer. The electronic absorption spectra of anaerobic Fe(II)-enzyme saturated with NO indicate interaction of NO. Consistent with the absorption data, electron paramagnetic resonance (EPR) spectra of Fe(II)-enzyme complexed with NO suggest NO binding to the EPR silent Fe(II) site giving rise to an EPR active species (g= 4.29, 3.95, 2.00). The rhombicity of the EPR spectrum is increased in the presence of DMSP, indicating that the substrate binds to iron site without displacing bound NO. While other DMSP lyases have been characterized, this is the first thorough study of how a metallocofactor is involved in the metal-dependent lyase reaction.

Biochemical, kinetic, and spectroscopic characterization of a promiscuous metal-dependent DMSP-lyase

249th National Meeting (2015)

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