In recent years, a number of bioorthogonal reactions have been developed, exemplified by click chemistry, that enable the efficient formation of a specific product, even within a highly complex chemical environment. While the exquisite selectivity and reliability of these transformations have led to their broad application in diverse research areas, they have proven to be particularly beneficial to biological studies. In this regard, the ability to rationally incorporate reactive tags onto a biomolecular target and subsequently achieve high selectivity in tag derivatization within a complex biological sample has revolutionized the toolbox that is available for addressing fundamental issues. Herein, an introduction to the impact of click chemistry and other bioorthogonal reactions on the study of biological systems is presented. This includes discussion of the philosophy behind click chemistry, the details and benefits of bioorthogonal reactions that have been developed, and examples of recent innovative approaches that have effectively exploited these transformations to study cellular processes. For the latter, the impacts of bioorthogonal reactions on drug design (i.e., in situ combinatorial drug design), biomolecule labeling and detection (site-specific derivatization of proteins, viruses, sugars, DNA, RNA, and lipids), and the recent strategy of activity-based protein profiling are highlighted.

Sulfatases, which cleave sulfate esters in biological systems, play a key role in regulating the sulfation states that determine the function of many physiological molecules. Sulfatase substrates range from small cytosolic steroids, such as estrogen sulfate, to complex cell-surface carbohydrates, such as the glycosaminoglycans. The transformation of these molecules has been linked with important cellular functions, including hormone regulation, cellular degradation, and modulation of signaling pathways. Sulfatases have also been implicated in the onset of various pathophysiological conditions, including hormone-dependent cancers, lysosomal storage disorders, developmental abnormalities, and bacterial pathogenesis. These findings have increased interest in sulfatases and in targeting them for therapeutic endeavors. Although numerous sulfatases have been identified, the wide scope of their biological activity is only beginning to emerge. Herein, accounts of the diversity and growing biological relevance of sulfatases are provided along with an overview of the current understanding of sulfatase structure, mechanism, and inhibition.

Human antibody 2G12 neutralizes a broad range of HIV-1 isolates. Hence, molecular characterization of its epitope, which corresponds to a conserved cluster of oligomannoses on the viral envelope glycoprotein gp120, is a high priority in HIV vaccine design. A prior crystal structure of 2G12 in complex with Man 9GlcNAc2 highlighted the central importance of the D1 arm in antibody binding. To characterize the specificity of 2G12 more precisely, we performed solution-phase ELISA, carbohydrate microarray analysis, and cocrystallized Fab 2G12 with four different oligomannose derivatives (Man 4, Man5, Man7, and Man8) that compete with gp120 for binding to 2G12. Our combined studies reveal that 2G12 is capable of binding both the D1 and D3 arms of the Man 9GlcNAc2 moiety, which would provide more flexibility to make the required multivalent interactions between the antibody and the gp120 oligomannose cluster than thought previously. These results have important consequences for the design of immunogens to elicit 2G12-like neutralizing antibodies as a component of an HIV vaccine. 2G12 antibody ͉ HIV vaccine ͉ oligomannoses There is widespread agreement that the most promising approach to contain the ongoing HIV pandemic is through the development of an effective vaccine (1, 2). However, HIV vaccine design has faced many difficulties including, prominently, the lack of an immunogen able to elicit broadly neutralizing antibodies (Abs). The feasibility of developing such an immunogen is suggested by a small panel of broadly neutralizing human monoclonal antibodies (mAbs) that have been isolated from seropositive donors (3). One of these Abs, 2G12, recognizes a conserved and unusually dense cluster of oligomannose residues on the ''silent face'' of gp120, the major envelope protein of HIV-1 (4, 5). Many lectins have been identified that can bind to envelope and act antivirally, but 2G12 remains the only known anti-carbohydrate protein that has been specifically elicited to HIV-1 in an adaptive immune response (6). 2G12 has an unusual architecture in which the arms of the IgG swap variable heavy domains, creating a domainswapped dimer of Fabs (7). The crystal structure of Fab 2G12 complexed with Man 9 GlcNAc 2 indicated that the conventional Ab-binding sites are occupied by the D1 arms of the Man 9 GlcNAc 2 moieties (1; Fig. 1) (7). The terminal Man␣1-2Man residues of the D1 branch account for 85% of the Fab contacts to Man 9 GlcNAc 2 , although the disaccharide by itself is 50-fold less potent in binding to 2G12 than Man 9 GlcNAc 2 (7).Based on these structural results, several initiatives have been launched to design novel immunogens that will elicit 2G12-like Abs (8-12). Recently, we described the design and synthesis of novel antigens, oligomannoses 2-6 (Fig. 1), that bind to mAb 2G12 (13). The Man␣1-2Man-containing oligomannoses 4, 5, and 6 were identified as new epitope mimics that inhibit the binding of gp120 to mAb 2G12 as well as, or better than, Man 9 GlcNAc 2 (13). Encouraged by this result, we now report the desig...

The sulfonation (also known as sulfurylation) of biomolecules has long been known to take place in a variety of organisms, from prokaryotes to multicellular species, and new biological functions continue to be uncovered in connection with this important transformation. Early studies of sulfotransferases (STs), the enzymes that catalyze sulfonation, focused primarily on the cytosolic STs, which are involved in detoxification, hormone regulation, and drug metabolism. Although known to exist, the membrane-associated STs were not studied as extensively until more recently. Involved in the sulfonation of complex carbohydrates and proteins, they have emerged as central players in a number of molecular-recognition events and biochemical signaling pathways. STs have also been implicated in many pathophysiological processes. As a result, much interest in the complex roles of STs and in their targeting for therapeutic intervention has been generated. Progress in the elucidation of the structures and mechanisms of sulfotransferases, as well as their biological activity, inhibition, and synthetic utility, are discussed in this Review.

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