The x-ray crystal structure of the tetrameric T-antigen-binding lectin from peanut, Mr 110,000, has been determined by using the multiple isomorphous replacement method and refined to an R value of 0.218 for 22,155 reflections within the 10-to 2.95-resolution range. Each subunit has essentially the same characteristic tertiary fold that is found in other legume lectins. The structure, however, exhibits an unusual quaternary arrangement of subunits. Unlike other well-characterized tetrameric proteins with identical subunits, peanut lectin has neither 222 (D2) nor fourfold (C4) symmetry. A noncrystallographic twofold axis relates two halves of the molecule. The two monomers in each half are related by a local twofold axis. The mutual disposition of the axes is such that they do not lead to a closed point group. Furthermore, the structure of peanut lectin demonstrates that differences in subunit arrangement in legume lectins could be due to factors intrinsic to the protein molecule and, contrary to earlier suggestions, are not necessarily caused by interactions involving covalently linked sugar. The structure provides a useful framework for exploring the structural basis and the functional implications of the variability in the subunit arrangement in legume lectins despite all of them having nearly the same subunit structure, and also for investigating the general problem of "open" quaternary assembly in oligomeric proteins.Lectins are multivalent proteins of nonimmune origin that bind cell surface carbohydrates with high specificity (1, 2). Although originally isolated from plant sources and characterized by their ability to agglutinate erythrocytes, lectins are now known to be ubiquitous in nature, with binding specificities for a wide variety of cells. They have received considerable attention in recent years on account of their use in studies on biological receptors and cell surface phenomena.The most extensively studied lectins are those obtained from the seeds of leguminous plants. These lectins are either dimeric or tetrameric. The first lectin to be x-ray analyzed, in the 1970s, was the tetrameric concanavalin A (Con A) from thejack bean (3, 4). The three-dimensional structures ofthree more lectins, those of pea lectin, favin, and isolectin I from the seeds ofLathyrus ochrus, became available subsequently (5-7). In the meantime, it was shown by several workers that legume lectins are related to one another by sequence homology (8). As is to be expected from the homology, the subunits in Con A, pea lectin, favin, and the L. ochrus lectin have nearly the same tertiary structure, although Con A has a single-chain subunit while the other three have two polypeptide chains in each subunit. They contain two metal ions each (calcium and manganese), which are situated in the same locations in the three-dimensional structures of the four lectins. The locations of the carbohydrate-binding region in them are also broadly similar. Furthermore, the lectin subunits dimerize in a similar fashion. The dimers further...

Click chemistry has played a significant role as a rapid and versatile strategy for conjugating two molecular fragments under very mild reaction conditions. Introduction of ferrocene-derived triazole systems using click chemistry has attracted enormous interest in various fields due to its potential applications in electrochemical techniques for detection and sensing. The present discussion focuses on the synthesis of ferrocene-triazole and the importance of using a CuAAC reaction for such conjugation. Applications of ferrocene-based click reactions in conjugate chemistry, asymmetric catalysis, medicinal chemistry, host-guest interactions, and materials chemistry have been highlighted.

In this work, a direct Z-scheme Cs2O–Bi2O3–ZnO heterostructure without any electron mediator is fabricated by a simple solution combustion route.

A comprehensive study of a general and effective one-step procedure for the synthesis of beta-sulfonamidodisulfides directly from N-tosyl aziridines in a regio- and stereospecific manner under neutral conditions without the use of any Lewis acid or base has been reported. This methodology is extended to the synthesis of an optically pure cyclic seven-membered disulfide 29. Synthesis of a variety of beta-sulfonamidosulfides involving tandem, multistep reactions in one pot is also reported.

No abstract