4pkc

Publication Abstract from PubMed

Anaerobic degradation of the environmental pollutant toluene is initiated by the glycyl radical enzyme benzylsuccinate synthase (BSS), which catalyzes the radical addition of toluene to fumarate, forming benzylsuccinate. We have determined crystal structures of the catalytic alpha-subunit of BSS with its accessory subunits beta and gamma, which both bind a [4Fe-4S] cluster and are essential for BSS activity in vivo. We find that BSSalpha has the common glycyl radical enzyme fold, a 10-stranded beta/alpha-barrel that surrounds the glycyl radical cofactor and active site. Both accessory subunits beta and gamma display folds related to high potential iron-sulfur proteins but differ substantially from each other in how they interact with the alpha-subunit. BSSgamma binds distally to the active site, burying a hydrophobic region of BSSalpha, whereas BSSbeta binds to a hydrophilic surface of BSSalpha that is proximal to the active site. To further investigate the function of BSSbeta, we determined the structure of a BSSalphagamma complex. Remarkably, we find that the barrel partially opens, allowing the C-terminal region of BSSalpha that houses the glycyl radical to shift within the barrel toward an exit pathway. The structural changes that we observe in the BSSalphagamma complex center around the crucial glycyl radical domain, thus suggesting a role for BSSbeta in modulating the conformational dynamics required for enzyme activity. Accompanying proteolysis experiments support these structural observations.

Structures of benzylsuccinate synthase elucidate roles of accessory subunits in glycyl radical enzyme activation and activity.,Funk MA, Judd ET, Marsh EN, Elliott SJ, Drennan CL Proc Natl Acad Sci U S A. 2014 Jun 30. pii: 201405983. PMID:24982148^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.