PDBsum entry 1kzc

Immune system, sugar binding protein

PDB id: 1kzc

Contents

Protein chains

111 a.a. *

Ligands

MAN ×2

Metals

_CL

_CA ×4

Waters ×241

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Orientation of bound ligands in mannose-Binding proteins. Implications for multivalent ligand recognition.

Authors

K.K.Ng, A.R.Kolatkar, S.Park-Snyder, H.Feinberg, D.A.Clark, K.Drickamer, W.I.Weis.

Ref.

J Biol Chem, 2002, 277, 16088-16095. [DOI no: 10.1074/jbc.M200493200]

PubMed id

11850428

Abstract

Mannose-binding proteins (MBPs) are C-type animal lectins that recognize high mannose oligosaccharides on pathogenic cell surfaces. MBPs bind to their carbohydrate ligands by forming a series of Ca(2+) coordination and hydrogen bonds with two hydroxyl groups equivalent to the 3- and 4-OH of mannose. In this work, the determinants of the orientation of sugars bound to rat serum and liver MBPs (MBP-A and MBP-C) have been systematically investigated. The crystal structures of MBP-A soaked with monosaccharides and disaccharides and also the structure of the MBP-A trimer cross-linked by a high mannose asparaginyl oligosaccharide reveal that monosaccharides or alpha1-6-linked mannose bind to MBP-A in one orientation, whereas alpha1-2- or alpha1-3-linked mannose binds in an orientation rotated 180 degrees around a local symmetry axis relating the 3- and 4-OH groups. In contrast, a similar set of ligands all bind to MBP-C in a single orientation. The mutation of MBP-A His(189) to its MBP-C equivalent, valine, causes Man alpha 1-3Man to bind in a mixture of orientations. These data combined with modeling indicate that the residue at this position influences the orientation of bound ligands in MBP. We propose that the control of binding orientation can influence the recognition of multivalent ligands. A lateral association of trimers in the cross-linked crystals may reflect interactions within higher oligomers of MBP-A that are stabilized by multivalent ligands.

Figure 1.
Fig. 1. Orientation of sugars bound in the MBP site. In A and B, the structure of the terminal mannose of the Man (1,2) branch of Man[6]GlcNAc[2]Asn (13) defining orientation I is shown on the left, and the structure of MeMan bound to MBP-C (14) defining orientation II is shown on the right. Ca^2+ coordination bonds are shown as long dashed lines, hydrogen bonds are shown as short dashed lines, and van der Waals contacts are shown as dotted lines. A, a view of the MBP binding site roughly perpendicular to the face of the pyranose ring. B, a view of the site rotated ~90° around the vertical axis with respect to A. For clarity, MBP-A residues His189 and Ile^207 and MBP-C residues Val194 and Val212 are shown only in B. The conformation of MBP-A His189 is determined by a hydrogen bond between His189 N[ 1] and the backbone NH of Gly191 (not shown).

Figure 2.
Fig. 2. Structures of native and monosaccharide-bound MBP-A. The view is the same as that shown in Fig. 1A. For clarity, His189 and Ile^207 are shown only if they form contacts with the bound ligand. A, native crystal cryopreserved in MPD, showing the two water molecules that form the seventh and eighth coordination bonds with the Ca 2+. B, MeMan. C, MeGlcNAc protomer A (orientation I). van der Waals contacts between C6 of the pyranose ring and Ile^207 are shown. D, MeGlcNAc protomer C (orientation II). van der Waals contacts between the acetamido-moiety and Ile^207 are shown. E, MeFuc. van der Waals contacts between the side chain of His189 and the anomeric oxygen are shown. F, MeFuc.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2002, 277, 16088-16095) copyright 2002.