Hackwon, Do; Kim, Soo Jin; Lee, Chang Woo; Kim, Han-Woo; Park, Hyun Ho; Kim, Ho Min; Park, Hyun; Park, HaJeung; Lee, Jun Hyuck
Crystal structure of UbiX, an aromatic acid decarboxylase from the psychrophilic bacterium Colwellia psychrerythraea that undergoes FMN-induced conformational changes
SCIENTIFIC REPORTS, 5 Art. No. 8196, FEB 3 2015

The ubiX gene of Colwellia psychrerythraea strain 34H encodes a 3-octaprenyl-4-hydroxybenzoate carboxylase (CpsUbiX, UniProtKB code: Q489U8) that is involved in the third step of the ubiquinone biosynthesis pathway and harbors a flavin mononucleotide (FMN) as a potential cofactor. Here, we report the crystal structures of two forms of CpsUbiX: an FMN-bound wild type form and an FMN-unbound V47S mutant form. CpsUbiX is a dodecameric enzyme, and each monomer possesses a typical Rossmann-fold structure. The FMN-binding domain of UbiX is composed of three neighboring subunits. The highly conserved Gly15, Ser41, Val47, and Tyr171 residues play important roles in FMN binding. Structural comparison of the FMN-bound wild type form with the FMN-free form reveals a significant conformational difference in the C-terminal loop region (comprising residues 170-176 and 195-206). Subsequent computational modeling and liposome binding assay both suggest that the conformational flexibility observed in the C-terminal loops plays an important role in substrate and lipid bindings. The crystal structures presented in this work provide structural framework and insights into the catalytic mechanism of CpsUbiX.


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