1de6
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L-RHAMNOSE ISOMERASE
OverviewOverview
Using a new expression construct, rhamnose isomerase from Escherichia coli, was purified and crystallized. The crystal structure was solved by, multiple isomorphous replacement and refined to a crystallographic, residual of 17.4 % at 1.6 A resolution. Rhamnose isomerase is a tight, tetramer of four (beta/alpha)(8)-barrels. A comparison with other known, structures reveals that rhamnose isomerase is most similar to xylose, isomerase. Alignment of the sequences of the two enzymes based on their, structures reveals a hitherto undetected sequence identity of 13 %, suggesting that the two enzymes evolved from a common precursor. The, structure and arrangement of the (beta/alpha)(8)-barrels of rhamnose, isomerase are very similar to xylose isomerase. Each enzyme does, however, have additional alpha-helical domains, which are involved in tetramer, association, and largely differ in structure. The structures of complexes, of rhamnose isomerase with the inhibitor l-rhamnitol and the natural, substrate l-rhamnose were determined and suggest that an extended loop, which is disordered in the native enzyme, becomes ordered on substrate, binding, and may exclude bulk solvent during catalysis. Unlike xylose, isomerase, this loop does not extend across a subunit interface but, contributes to the active site of its own subunit. It illustrates how an, interconversion between inter and intra-subunit complementation can occur, during evolution. In the crystal structure (although not necessarily in, vivo) rhamnose isomerase appears to bind Zn(2+) at a "structural" site. In, the presence of substrate the enzyme also binds Mn(2+) at a nearby, "catalytic" site. An array of hydrophobic residues, not present in xylose, isomerase, is likely to be responsible for the recognition of l-rhamnose, as a substrate. The available structural data suggest that a, metal-mediated hydride-shift mechanism, which is generally favored for, xylose isomerase, is also feasible for rhamnose isomerase.
About this StructureAbout this Structure
1DE6 is a Single protein structure of sequence from Escherichia coli with RNS, ZN and MN as ligands. Active as L-rhamnose isomerase, with EC number 5.3.1.14 Full crystallographic information is available from OCA.
ReferenceReference
The structure of rhamnose isomerase from Escherichia coli and its relation with xylose isomerase illustrates a change between inter and intra-subunit complementation during evolution., Korndorfer IP, Fessner WD, Matthews BW, J Mol Biol. 2000 Jul 21;300(4):917-33. PMID:10891278
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