1BYF

STRUCTURE OF TC14; A C-TYPE LECTIN FROM THE TUNICATE POLYANDROCARPA MISAKIENSIS

Summary for 1BYF

• Entry DOI: 10.2210/pdb1byf/pdb
• Descriptor: PROTEIN (POLYANDROCARPA LECTIN), CALCIUM ION, ZINC ION, ... (6 entities in total)
• Functional Keywords: c-type lectin, galactose-specific, sugar binding protein
• Biological source: Polyandrocarpa misakiensis
• Total number of polymer chains: 2
• Total formula weight: 29123.55

Authors

Poget, S.F.,Legge, G.B.,Bycroft, M.,Williams, R.L. (deposition date: 1998-10-14, release date: 1999-07-23, Last modification date: 2024-10-30)

Primary citation

Poget, S.F.,Legge, G.B.,Proctor, M.R.,Butler, P.J.,Bycroft, M.,Williams, R.L.
The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose.
J.Mol.Biol., 290:867-879, 1999

PubMed Abstract: 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.

PubMed: 10398588
DOI: 10.1006/jmbi.1999.2910

Experimental method

X-RAY DIFFRACTION (2 Å)