PDBsum entry 1tlg

Lectin

PDB id: 1tlg

Contents

Protein chains

123 a.a. *

Ligands

GAL ×2

Metals

_ZN ×5

_CA ×4

Waters ×243

* Residue conservation analysis

PDB id:

1tlg

Name:

Lectin

Title:

Structure of a tunicatE C-type lectin complexed with d-galactose

Structure:

Polyandrocarpa lectin. Chain: a, b. Synonym: tc14. Engineered: yes

Source:

Polyandrocarpa misakiensis. Organism_taxid: 7723. Expressed in: escherichia coli. Expression_system_taxid: 562. Expression_system_variant: c41. Other_details: synthetic gene

Biol. unit:

Dimer (from PQS)

Resolution:

2.20Å R-factor: 0.211 R-free: 0.269

Authors:

S.F.Poget,G.B.Legge,M.Bycroft,R.L.Williams

Key ref:

S.F.Poget et al. (1999). The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose. J Mol Biol, 290, 867-879. PubMed id: 10398588 DOI: 10.1006/jmbi.1999.2910

Date:

16-Oct-98 Release date: 23-Jul-99

Protein chains

P16108  (LECC_POLMI) -  Lectin from Polyandrocarpa misakiensis

Seq: 125 a.a.

Struc: 123 a.a.

DOI no: 10.1006/jmbi.1999.2910

J Mol Biol 290:867-879 (1999)

PubMed id: 10398588

The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose.

S.F.Poget, G.B.Legge, M.R.Proctor, P.J.Butler, M.Bycroft, R.L.Williams.

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.

Selected figure(s)

Figure 5.
Figure 5. Ribbon diagram of the TC14 dimer. All elements of secondary structure are labelled in the upper molecule, and labelling is repeated for some elements in the lower molecule to improve clarity. The sugar-binding calcium ions are shown as grey spheres and the galactose molecules in a ball-and-stick representation.

Figure 6.
Figure 6. Representation of the hydrophobic interactions at the dimeric interface. The phenylalanine residues involved in hydrophobic contacts are shown in ball-and-stick representations. Molecule A is shown in light grey and molecule B in dark grey.

The above figures are reprinted by permission from Elsevier: J Mol Biol (1999, 290, 867-879) copyright 1999.

Figures were selected by an automated process.