1mn0: Difference between revisions

[[Image:1mn0.jpg|left|200px]]<br /><applet load="1mn0" size="350" color="white" frame="true" align="right" spinBox="true"  

Galactose mutarotase catalyzes the conversion of beta-D-galactose to alpha-D-galactose in the Leloir pathway for galactose metabolism. The high resolution x-ray structure of the dimeric enzyme from Lactococcus lactis was recently solved and shown to be topologically similar to the 18-stranded, anti-parallel beta-motif observed for domain 5 of beta-galactosidase. In addition to determining the overall molecular fold of galactose mutarotase, this initial investigation also provided a detailed description of the electrostatic interactions between the enzyme and its physiologically relevant substrate, galactose. Specifically, the side chains of His-96 and His-170 were shown to be located within hydrogen bonding distance to the C-5 oxygen of the substrate, while the carboxylate of Glu-304 was positioned near the C-1 hydroxyl group of the sugar. On the basis of this initial study, a possible role for Glu-304 as the general acid/base group in catalysis was put forth. Here we describe the combined x-ray crystallographic and kinetic analyses of L. lactis galactose mutarotase complexed with D-glucose, D-fucose, D-quinovose, L-arabinose, or D-xylose. These investigations have revealed that there are several distinct binding modes for these sugars, which are dependent upon the spatial orientation of the C-4 hydroxyl group. In those sugars with the same C-4 hydroxyl group orientation as galactose, their C-1 hydroxyl groups are invariably located near Glu-304. For those sugars, which have the same C-4 hydroxyl group configuration as glucose, the C-1 hydroxyls are typically located near Asp-243. These different binding modes correlate with both the observed kinetic parameters and the presence or absence of a hydrogen bond between the guanidinium group of Arg-71 and the C-4 hydroxyl group of the sugar ligand.

1MN0 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Lactococcus_lactis Lactococcus lactis] with <scene name='pdbligand=XYS:'>XYS</scene> and <scene name='pdbligand=NI:'>NI</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Aldose_1-epimerase Aldose 1-epimerase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=5.1.3.3 5.1.3.3] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1MN0 OCA].  

[[Category: Holden, H M.]]

[[Category: Raushel, F M.]]

[[Category: Thoden, J B.]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 13:56:50 2008''