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].
References
1
Kadokura,
H., Katzen, F. and Beckwith, J. (2003) Annu. Rev. Biochem. 72, 111-135.
2
Bardwell,
J.C., Lee, J.O., Jander, G., Martin, N., Belin, D. and Beckwith, J. (1993) Proc.
Natl. Acad. Sci. USA 90, 1038-1042.
3
Rietsch,
A., Belin, D. Martin, N. and Beckwith, J. (1996) Proc. Natl. Acad. Sci. USA 93, 13048-13053.
4
Martin,
J.L., Bardwell, J.C. and Kuriyan, J. (1993) Nature 365, 464-468.
5 McCarthy, A.A., Haebel, P.W., Torronen, A., Rybin, V., Baker, E.N. and Metcalf, P. (2000) Nature Struct. Biol. 7, 196Ğ199.
6
Edeling,
M.A., Guddat, L.W., Fabianek, R.A., Thšny-Meyer, L. and Martin, J.L. (2002) Structure 10, 973-979.
7
Shao, F.,
Bader, M.W., Jakob, U. and Bardwell, J.C. (2000) J. Biol. Chem. 275, 13349-13352.
8
Heras, B.,
Edeling, M.A., Byriel, K.A., Jones, A., Raina, S. and Martin, J.L. (2003) Structure 11, 139-145.
9
Haebel PW,
Goldstone D, Katzen F, Beckwith J, Metcalf P. (2002) EMBO J. 21, 4774-4784.