UDP-Sulfoquinovose
Synthase (SQD1)
from A.
thaliana
|
Ribbon drawing of
UDP-sulfoquinovose synthase (SQD1) with bound NAD and UDP-glucose. SQD1 is
involved in the biosynthesis of the unique sulfolipid SQDG found in plants
and many photosynthetic bacteria. |
A Gallery of SDR Enzymes
|
This
gallery of ribbon drawings show the structural relationships between the
small NAD(P)-dependent dehydrogenase (SDR) subfamily and and the larger
reductase/epimerase/dehydratase (RED) family. All these enzymes have a
Rossmann fold (blue), a substrate-binding loop (yellow), a helix-strand
addition to the Rossmann fold (green) to make a 6+1 stranded sheet, and a
C-terminal tail (copper) which often can create a more extensive substrate
binding site. |
GDP-4',6'-mannose dehydratase MUR1 from A. thaliana
|
Unlike many of the RED and SDR
enzymes, the GDP-4',6'-mannose dehydratase MUR1 is a tetramer where the
NADP(H) cofactor binding sites are interacting. In this tetramer, three
of the active sites are occupied with NADP(H) and GDP-rhamnose (a dead-end
enzymatic by-product), but one monomer does not bind GDP-rhamnose.
Further evidence suggests that the "empty" active site has
lower affinity for GDP'-sugars and may indicate negative cooperativity.
The one monomer (subunit C) with the "empty" active site (i.e., containing only NADPH ) has an open conformation, while the fully occupied active sites with NADP(H) and GDP-rhamnose (subunits A, B, and D) have a closed conformation. References of interest Mulichak, A. M., Theisen, M. J., Essigmann, B., Benning, C., and Garavito,
R. M. (1999) "Crystal structure of SQD1, an enzyme involved in the
biosynthesis of the plant sulfolipid headgroup donor UDP-sulfoquinovose."
Proc. Natl. Acad. Sci. USA 96, 13097-102. Sanda, S., Leustek, T., Theisen, M. J., Garavito, R. M., and Benning, C.
(2001) Recombinant Arabidopsis SQD1 converts UDP-glucose and sulfite to the
sulfolipid headgroup precursor UDP-sulfoquinovose. J. Biol. Chem. 276,
3941-3946. Mulichak , A. M., C. P. Bonin, W.-D. Reiter, and R. M. Garavito (2002)
"The Structure of the MUR1 GDP-mannose 4,6-dehydratase from A. thaliana:
Implications for Ligand Binding Specificity." Biochemistry 41, 15578-89. Webb, Nicole A., Mulichak, Anne M., Lam, Joseph
S., Rocchetta, Heather L., and Garavito, R. M. (2004) “Crystal Structure of a
Tetrameric GDP-D-mannose 4,6-dehydratase from a Bacterial GDP-D-rhamnose
Biosynthetic Pathway.” Protein Sci., 13, 529-39. Shimojima, M., Hoffmann-Benning, S., Garavito, R. M., and Benning, C.
(2005) “Ferredoxin-dependent glutamate synthase moonlights in plant
sulfolipid biosynthesis by forming a complex with SQD1.” Arch. Biochem.
Biophys. 436, 206-14. |
