Goel M, Anuradha P, Kaur K J, Maiya B G, Swamy M J, Salunke D M
National Institute of Immunology, New Delhi 110067, India.
Acta Crystallogr D Biol Crystallogr. 2004 Feb;60(Pt 2):281-8. doi: 10.1107/S0907444903026684. Epub 2004 Jan 23.
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.
已在1.8埃分辨率下测定了中-四磺酸苯基卟啉（H(2)TPPS）与波罗蜜（Artocarpus integriflora）凝集素（jacalin）复合物的晶体结构。在晶体中，一对卟啉夹在两个对称相关的jacalin单体之间，形成了蛋白质分子的交联网络。除了堆积相互作用外，H(2)TPPS还在碳水化合物结合位点与jacalin形成氢键，其中一些涉及水桥。赋予jacalin半乳糖吡喃糖苷特异性的残基会发生构象调整，以容纳H(2)TPPS分子。jacalin碳水化合物结合位点的水分子巩固了jacalin-卟啉相互作用，优化了它们的互补性。与半乳糖吡喃糖苷和jacalin之间的相互作用相比，卟啉与jacalin的相互作用相对较弱，这可能是因为前者主要涉及水介导的氢键。虽然H(2)TPPS与ConA一样在碳水化合物结合位点与jacalin结合，但其与jacalin的相互作用模式非常不同。H(2)TPPS不会进入jacalin的碳水化合物结合腔。相反，它位于结合位点上方。在ConA的情况下，卟啉结合是通过磺酸根原子复制甘露糖吡喃糖苷的氢键网络介导的，而在jacalin的情况下，与碳水化合物结合位点相关的可塑性通过完全不同的一组相互作用来容纳多能性的卟啉分子。
