PSD-95/SAP90 is a member of the MAGUK superfamily. In excitatory synapses, PSD-95 clusters receptors and ion channels at specific sites in the postsynaptic membrane and organizes downstream signaling and cytoskeletal molecules. We have determined the crystal structures of the apo and GMP-bound forms to 2.3 and 2.0 A resolutions, respectively, of a fragment containing the SH3, HOOK, and guanylate kinase (GK) domains of PSD-95. We observe an intramolecular interaction between the SH3 and GK domains involving the formation of a beta sheet including residues N- and C-terminal to the GK domain. Based on amino acid conservation and mutational data available in the literature, we propose that this intramolecular interaction is a common feature among MAGUK proteins.
The intracellular parasite Trypanosoma cruzi, the etiological agent of Chagas disease, sheds a developmentally regulated surface trans-sialidase, which is involved in key aspects of parasite-host cell interactions. Although it shares a common active site architecture with bacterial neuraminidases, the T.cruzi enzyme behaves as a highly efficient sialyltransferase. Here we report the crystal structure of the closely related Trypanosoma rangeli sialidase and its complex with inhibitor. The enzyme folds into two distinct domains: a catalytic β-propeller fold tightly associated with a lectin-like domain. Comparison with the modeled structure of T.cruzi trans-sialidase and mutagenesis experiments allowed the identification of amino acid substitutions within the active site cleft that modulate sialyltransferase activity and suggest the presence of a distinct binding site for the acceptor carbohydrate. The structures of the Trypanosoma enzymes illustrate how a glycosidase scaffold can achieve efficient glycosyltransferase activity and provide a framework for structure-based drug design.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.