Structural basis for the recognition of complex‐type biantennary oligosaccharides by Pterocarpus angolensis lectin

Abstract

Lectins (or lectin domains) represent a specific class of carbohydrate binding proteins distinct from enzymes and antibodies. Different lectin families are found in a wide range of organisms including viruses, bacteria, plants and animals. Their biological activities are diverse and include roles in the innate immunity, bacterial and viral infection, sorting and trafficking of glycoproteins, development and differentiation as well as defense mechanisms in plants [1].The lectins from legume plants belong to one of the best studied lectin families [2]. Members of this family were initially identified in the seeds of legume plants, but an increasingly larger number is found in the vegetative parts. They show strong similarities on the level of their amino acid sequences and tertiary structures, and exhibits a wide range of carbohydrate specificities and quaternary structures. Recently, family members were discovered in nonlegume plants [3]. Furthermore, the ER-Golgi intermediate (ERGIC) proteins that in animals play a role in glycoprotein transport though the golgi apparatus (but are absent in plants) belong to the legume lectin family [4].Concanavalin A (con A) was the first lectin for which the crystal structure was determined [5,6]. Since this early work, the crystal structures of 28 members of the legume lectin family have been presented either The crystal structure of Pterocarpus angolensis lectin is determined in its ligand-free state, in complex with the fucosylated biantennary complex type decasaccharide NA2F, and in complex with a series of smaller oligosaccharide constituents of NA2F. These results together with thermodynamic binding data indicate that the complete oligosaccharide binding site of the lectin consists of five subsites allowing the specific recognition of the pentasaccharide GlcNAcb(1-2)Mana(1-3)[GlcNAcb(1-2)Mana(1-6)]Man. The mannose on the 1-6 arm occupies the monosaccharide binding site while the GlcNAc residue on this arm occupies a subsite that is almost identical to that of concanavalin A (con A). The core mannose and the GlcNAcb(1-2)Man moiety on the 1-3 arm on the other hand occupy a series of subsites distinct from those of con A. AbbreviationsCon A, concanavalin A; ITC, isothermal titration calorimetry; LOL, Lathyrus ochrus lectin.

How a Plant Lectin Recognizes High Mannose Oligosaccharides

“…The carbohydrate-binding site of subunit A is involved in crystal packing and therefore limits the conformations that are accessible to the bound carbohydrate. After the desoaking step (see ''Materials and Methods''), a molecule of Mana(1-3)Man remains bound (Loris et al, 2005), but in a number of cases this can still be substituted by a different carbohydrate ligand if the concentration of the replacing ligand is sufficiently high (Loris et al, 2003(Loris et al, , 2004Buts et al, 2006). The interactions and carbohydrate conformations observed in this binding site then have to be interpreted as situations that are possible in solution, but not necessarily reflecting the dominant one.…”

“…To produce complexes with high Man oligosaccharides, these crystals were first desoaked by transferring them to artificial mother liquor devoid of sugar (100 mM Na-cacodylate pH 6.5, 200 mM Ca-acetate, 20% [w/v] PEG-8000) for (Loris et al, 2005;Buts et al, 2006). Desoaked crystals were then transferred to 1 mL drops containing 20 mg of the desired sugar.…”

“…The first one concerns lectins in complex with a fucosylated or nonfucosylated complex-type biantennary oligosaccharide or with the pentasaccharide GlcNAcb (1-2)Mana(1-3)[GlcNAcb(1-2)Mana(1-6)]Man derived thereof. They include the legume lectins Lathyrus ochrus lectin, concanavalin A (con A) and Pterocarpus angolensis seed lectin (PAL; Bourne et al, 1994b;Moothoo and Naismith, 1998;Buts et al, 2006), bovine galectin 1 (Bourne et al, 1994a), and DC-SIGN, a C-type lectin (Feinberg et al, 2001). The second group concerns sialylated pentasaccharides recognized by cholera toxin (Merritt et al, 1994) and influenza virus hemagglutinin (Ha et al, 2003;Gamblin et al, 2004).…”

“…Exceptions are the interactions of high Man oligosaccharides with con A (Mandal et al, 1994), cyanovirin-N , and the human antibody 2G12 (Wang et al, 2004), of the pentasaccharide GlcNAcb(1-2)Mana(1-3) [GlcNAcb(1-2)Mana(1-6)]Man with PAL, con A, and other Diocleinae lectins (Mandal et al, 1994;Dam et al, 1998;Buts et al, 2006) and of bivalent pentasaccharides and sialofetuin with different galectins (Ahmad et al, 2004;Dam et al, 2005). Only for con A, PAL, and cyanovirin-N is at least one corresponding crystal structure available.…”

A Lectin from Platypodium elegans with Unusual Specificity and Affinity for Asymmetric Complex N-Glycans

“…the agglutinin from Pterocarpus angolensis seed (PAL). 4 Crystallography and thermodynamic studies demonstrated high affinity for both oligomannose N-glycans and for biantennary complex type, correlated with the presence of an unusually extended binding region close to the primary binding site (17)(18)(19)(20).…”