Porphyrin binding to jacalin is facilitated by the inherent plasticity of the carbohydrate-binding site: novel mode of lectin-ligand interaction.
The crystal structure of the complex of meso-tetrasulfonatophenylporphyrin (H(2)TPPS) with jack fruit (Artocarpus integriflora) agglutinin (jacalin) has been determined at 1.8 A resolution. A porphyrin pair is sandwiched between two symmetry-related jacalin monomers in the crystal, leading to a cross-linking network of protein molecules. Apart from the stacking interactions, H(2)TPPS also forms hydrogen bonds, some involving water bridges, with jacalin at the carbohydrate-binding site. The residues that are involved in rendering galactopyranoside specificity to jacalin undergo conformational adjustments in order to accommodate the H(2)TPPS molecule. The water molecules at the carbohydrate-binding site of jacalin cement the jacalin-porphyrin interactions, optimizing their complementarity. Interactions of porphyrin with jacalin are relatively weak compared with those observed between galactopyranoside and jacalin, perhaps because the former largely involves water-mediated hydrogen bonds. While H(2)TPPS binds to jacalin at the carbohydrate-binding site as in the case of ConA, its mode of interaction with jacalin is very different. H(2)TPPS does not enter the carbohydrate-binding cavity of jacalin. Instead, it sits over the binding site. While the porphyrin binding is mediated by replicating the hydrogen-bonding network of mannopyranoside through the sulfonate atoms in the case of ConA, the plasticity associated with the carbohydrate-binding site accommodates the pluripotent porphyrin molecule in the case of jacalin through an entirely different set of interactions.
Goel
M
M
National Institute of Immunology, New Delhi 110067, India.
Anuradha
P
P
Kaur
K J
KJ
Maiya
B G
BG
Swamy
M J
MJ
Salunke
D M
DM
D001665:Binding Sites; D002241:Carbohydrates / Q000737:chemistry*; D004583:Electrons; D005690:Galactose / Q000737:chemistry; D006860:Hydrogen Bonding; D037102:Lectins / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D037121:Plant Lectins / Q000737:chemistry*; D010940:Plant Proteins / Q000378:metabolism; D011166:Porphyrins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D014961:X-Ray Diffraction
D002241:Carbohydrates; D037102:Lectins; D008024:Ligands; D037121:Plant Lectins; D010940:Plant Proteins; D011166:Porphyrins; C043696:jacalin; D005690:Galactose