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| {{STRUCTURE_1tlg| PDB=1tlg | SCENE= }} | | {{STRUCTURE_1tlg| PDB=1tlg | SCENE= }} |
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| '''STRUCTURE OF A TUNICATE C-TYPE LECTIN COMPLEXED WITH D-GALACTOSE'''
| | ===STRUCTURE OF A TUNICATE C-TYPE LECTIN COMPLEXED WITH D-GALACTOSE=== |
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| ==Overview==
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| 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.
| | The line below this paragraph, {{ABSTRACT_PUBMED_10398588}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 10398588 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_10398588}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Carbohydrate binding]] | | [[Category: Carbohydrate binding]] |
| [[Category: Galactose-specific]] | | [[Category: Galactose-specific]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 10:05:47 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 02:53:53 2008'' |
