The Role of Nanometer-Scaled Ligand Patterns in Polyvalent Binding by Large Mannan-Binding Lectin Oligomers

Abstract

Mannan-binding lectin (MBL) is an important protein of the innate immune system and protects the body against infection through opsonization and activation of the complement system on surfaces with an appropriate presentation of carbohydrate ligands. The quaternary structure of human MBL is built from oligomerization of structural units into polydisperse complexes typically with three to eight structural units, each containing three lectin domains. Insight into the connection between the structure and ligand-binding properties of these oligomers has been lacking. In this article, we present an analysis of the binding to neoglycoprotein-coated surfaces by size-fractionated human MBL oligomers studied with small-angle x-ray scattering and surface plasmon resonance spectroscopy. The MBL oligomers bound to these surfaces mainly in two modes, with dissociation constants in the micro to nanomolar order. The binding kinetics were markedly influenced by both the density of ligands and the number of ligand-binding domains in the oligomers. These findings demonstrated that the MBL-binding kinetics are critically dependent on structural characteristics on the nanometer scale, both with regard to the dimensions of the oligomer, as well as the ligand presentation on surfaces. Therefore, our work suggested that the surface binding of MBL involves recognition of patterns with dimensions on the order of 10–20 nm. The recent understanding that the surfaces of many microbes are organized with structural features on the nanometer scale suggests that these properties of MBL ligand recognition potentially constitute an important part of the pattern-recognition ability of these polyvalent oligomers.

Enhancement of Ebola Virus Infection via Ficolin-1 Interaction with the Mucin Domain of GP Glycoprotein

“…Comparable results were obtained with the C-type lectin domain of MBL (Fig. 2C), as observed previously for the binding of MBL oligomers and the MBL lectin domain to mannose-conjugated BSA (52). These data suggest that the efficient binding of ficolin-1 (and of MBL) to GP requires oligomerization of the recognition protein, which promotes avidity through a multivalent interaction.…”

“…Recombinant MBL, produced and purified as described previously (50), was kindly provided by NatImmune (Copenhagen, Denmark). The trimeric FBG recognition domain of ficolin-1 (FBG) and the C-type lectin carbohydrate recognition domain of MBL (MBL-CLec) were expressed in a baculovirus/insect cell system and purified as described previously (51,52). The molecular sizes of the proteins were estimated to be as follows: 388.1 kDa for ficolin-1, 305 kDa for MBL, 73.6 kDa for ficolin-1 FBG, and 49.1 kDa for MBL-CLec.…”

Secondary Cell Wall Polymers of Enterococcus faecalis Are Critical for Resistance to Complement Activation via Mannose-binding Lectin

“…Binding of the polyvalent oligomer MBL, however, is highly sensitive to the scaling of its binding domains. Rearrangement of its ligands even in the nanometer range strongly affects its interaction (49). Hence, WTA may mediate resistance to MBL indirectly by acting as a scaffold for other glycopolymers.…”

Deciphering Complement Receptor Type 1 Interactions with Recognition Proteins of the Lectin Complement Pathway

“…Indeed, longer collagen-like regions are expected to bring more flexibility, which could facilitate interactions involving the collagen stalks. Although no structural data are available regarding soluble ficolins, recent studies using solution X-ray scattering of MBL oligomers revealed highly flexible molecules with near planar fan-like structures in some instances (42,43). Moreover, MBL bound to surface ligands was shown to adopt a stretched conformation, as shown by atomic force microscopy (44).…”