Structure of Burkholderia cepacia UDP-glucose dehydrogenase (BceC) structure and the role of Tyr10 in the final hydrolysis of UGDs thioester intermediate

Joana Rocha; Alma Oltea; Patrícia Borges; Dalila Madeira Nascimento; Leonilde M. Moreira; Isabel Maria de Sá Correia Leite de; Arsénio do Carmo Sales Mendes Fialho; Carlos Frazão

Key information

Authors:

Joana Rocha; Alma Oltea (Alma Oltea Popescu); Patrícia Borges; Dalila Madeira Nascimento (Dalila Madeira Nascimento Mil-Homens); Leonilde M. Moreira (Leonilde de Fátima Morais Moreira); Isabel Maria de Sá Correia Leite de (Isabel Sá-Correia); Arsénio do Carmo Sales Mendes Fialho (Arsénio do Carmo Sales Mendes Fialho); Carlos Frazão

Published in

August 2011

Abstract

Members of the Burkholderia cepacia complex (BCC) are serious respiratory pathogens in immunocompromised individuals and in patients with cystic fibrosis (CF). They are exceptionally resistant to many antimicrobial agents and have the capacity to spread between patients, leading to a decline in lung function and necrotizing pneumonia. BCC members often express a mucoid phenotype associated with the secretion of the exopolysaccharide (EPS) cepacian. There is much evidence supporting the fact that cepacian is a major virulence factor of BCC. UDP-glucose dehydrogenase (UGD) is responsible for the NAD-dependent 2-fold oxidation of UDP-glucose (UDP-Glc) to UDP-glucuronic acid (UDP-GlcA), which is a key step in cepacian biosynthesis. Here, we report the structure of BceC, determined at 1.75-Å resolution. Mutagenic studies were performed on the active sites of UGDs, and together with the crystallographic structures, they elucidate the molecular mechanism of this family of sugar nucleotide-modifying enzymes. Superposition with the structures of human and other bacterial UGDs showed an active site with high structural homology. This family contains a strictly conserved tyrosine residue (Y10 in BceC; shown in italics) within the glycine-rich motif (GXGYXG) of its N-terminal Rossmann-like domain. We constructed several BceC Y10 mutants, revealing only residual dehydrogenase activity and thus highlighting the importance of this conserved residue in the catalytic activity of BceC. Based on the literature of the UGD/GMD nucleotide sugar 6-dehydrogenase family and the kinetic and structural data we obtained for BceC, we determined Y10 as a key catalytic residue in a UGD rate-determining step, the final hydrolysis of the enzymatic thioester intermediate.