CRYSTAL STRUCTURE OF DSBG A DISULFIDE BOND ISOMERASE FROM ESCHERICHIA COLI

 

Bego–a Heras,a Melissa A. Edeling,a Jennifer L. Martina and Satish Rainab

 

aInstitute for Molecular Bioscience, University of Queensland, Brisbane QLD 4072 Australia; bCentre Mdical Universitaire, Dpartement de Biochimie Mdicale, 1 Rue Michel-Servet, 1211 Genve 4, Switzerland (b.heras@imb.uq.edu.au)

 

 

The correct formation of disulfide bonds is important for the folding and function of many secretory and membrane proteins. In bacteria, disulfide bond formation occurs in the periplasmic space and is catalysed by the Dsb (disulfide bond formation) family of proteins (DsbA, DsbB, DsbC, DsbD, DsbE, and DsbG) [1]. These proteins form two distinct pathways for disulfide formation and rearrangement. The DsbA-DsbB pathway [2] rapidly introduces disulfide bonds into target proteins, sometimes resulting in the formation of nonnative disulfide bonds, whereas the DsbC/DsbG-DsbD pathway [3] catalyzes the rearrangement of incorrect disulfide bonds, allowing proteins to fold correctly.

Crystal structures of three Dsb proteins have been determined, DsbA, DsbC and DsbE [4-6]. Here we present the crystal structure of the last soluble member of the Dsb family, DsbG, a disulfide bond isomerase from E. coli that also functions as a molecular chaperone [7]. DsbG crystal structure determination required dehydration of crystals prior to data collection. This post-growth treatment dramatically improved the diffraction resolution of DsbG crystals from 10 to 2 (1.7 at a synchrotron source) [8]. The crystal structure of DsbG was determined by multiwavelength anomalous diffraction (MAD) methods and refined to an R free of 20.5% (R factor 18.8%) at 1.7 .

The overall structure of DsbG resembles that of DsbC [5]. Both are V-shaped homodimers in which each monomer incorporates an N-terminal dimerisation domain and a thioredoxin like catalytic domain separated by a linker a-helix. However, a striking difference between the two is the length of the linker helix located between the dimerisation and catalytic domain in each monomer, which is 2.5 turns longer in DsbG. This changes the characteristics of the hydrophobic cleft between the two monomers which is thought to be the binding site for unfolded proteins [9].

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