Codename Q : Enzymatic Double Agent

at where double-stranded DNA might fit into the picture will be of primary interest. Jason G. Underwood, Ph.D. “Sweeter” Proteins Post-translational modification of serines and threonines by N-acetylglucosamine (O-GlcNAc) is an important regulator of various cellular events, and misregulation of this process has been linked to diseases such as diabetes and Alzheimer’s disease. The enzyme O-GlcNAcase (OGA) is responsible for removing OGlcNAc from proteins; thus, OGA inhibitors effectively “sweeten” proteins by preventing the removal of OGlcNAc groups from their surface. These inhibitors are useful tools for deciphering the role of this modification, but development of potent and selective compounds has been challenging. Dorfmueller et al. ( J. Am. Chem. Soc. 2006, 128, 16,484-16,485) use the crystal structure of OGA in complex with the known inhibitor PUGNAc to guide the design of a novel OGA inhibitor termed GlcNAcstatin. Scrutiny of the OGA-PUGNAc complex revealed the presence of a deep pocket not present in the related enzymes human lysosomal hexosaminidases HexA and HexB. In addition, the authors noted that glycoimidazoles were effective mimics of the transition state of the sugar ring in the natural substrate of OGA. Mingling these two notions led to the design and synthesis of GlcNAcstatin, a glucoimidazole with structural similarities to PUGNAc but incorporating a larger isobutanamido group intended to occupy the OGA pocket. GlcNAcstatin was found to be a picomolar inhibitor of OGA and 100,000× more selective for OGA than for HexA and HexB. Determination of the crystal structure of GlcNAcstatin in complex with OGA further characterized the molecular details of the interaction. Finally, the compound was demonstrated to be a more effective GlcNAcase inhibitor than PUGNAc, as assessed by its ability to prevent the removal of O-GlcNAc from proteins in cell lysates and to raise O-GlcNAc levels in a human cancer cell line. These studies will facilitate development of additional tools to study this important cellular process, indeed sweetening the prospects for future O-GlcNAcylation investigations. Eva J. Gordon, Ph.D. 12 nm