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'''STRUCTURE OF TC14; A C-TYPE LECTIN FROM THE TUNICATE POLYANDROCARPA MISAKIENSIS''' | '''STRUCTURE OF TC14; A C-TYPE LECTIN FROM THE TUNICATE POLYANDROCARPA MISAKIENSIS''' | ||
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[[Category: Poget, S F.]] | [[Category: Poget, S F.]] | ||
[[Category: Williams, R L.]] | [[Category: Williams, R L.]] | ||
[[Category: | [[Category: C-type lectin]] | ||
[[Category: | [[Category: Galactose-specific]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 12:06:54 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 12:06, 2 May 2008
STRUCTURE OF TC14; A C-TYPE LECTIN FROM THE TUNICATE POLYANDROCARPA MISAKIENSIS
OverviewOverview
C-type lectins are calcium-dependent carbohydrate-recognising proteins. Isothermal titration calorimetry of the C-type Polyandrocarpa lectin (TC14) from the tunicate Polyandrocarpa misakiensis revealed the presence of a single calcium atom per monomer with a dissociation constant of 2.6 microM, and confirmed the specificity of TC14 for D -galactose and related monosaccharides. We have determined the 2.2 A X-ray crystal structure of Polyandrocarpa lectin complexed with D -galactose. Analytical ultracentrifugation revealed that TC14 behaves as a dimer in solution. This is reflected by the presence of two molecules in the asymmetric unit with the dimeric interface formed by antiparallel pairing of the two N-terminal beta-strands and hydrophobic interactions. TC14 adopts a typical C-type lectin fold with differences in structure from other C-type lectins mainly in the diverse loop regions and in the second alpha-helix, which is involved in the formation of the dimeric interface. The D -galactose is bound through coordination of the 3 and 4-hydroxyl oxygen atoms with a bound calcium atom. Additional hydrogen bonds are formed directly between serine, aspartate and glutamate side-chains of the protein and the sugar 3 and 4-hydroxyl groups. Comparison of the galactose binding by TC14 with the mannose binding by rat mannose-binding protein reveals how monosaccharide specificity is achieved in this lectin. A tryptophan side-chain close to the binding site and the distribution of hydrogen-bond acceptors and donors around the 3 and 4-hydroxyl groups of the sugar are essential determinants of specificity. These elements are, however, arranged in a very different way than in an engineered galactose-specific mutant of MBPA. Possible biological functions can more easily be understood from the fact that TC14 is a dimer under physiological conditions.
About this StructureAbout this Structure
1BYF is a Single protein structure of sequence from Polyandrocarpa misakiensis. Full crystallographic information is available from OCA.
ReferenceReference
The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose., Poget SF, Legge GB, Proctor MR, Butler PJ, Bycroft M, Williams RL, J Mol Biol. 1999 Jul 23;290(4):867-79. PMID:10398588 Page seeded by OCA on Fri May 2 12:06:54 2008