August 2009 news and views

Research highlights

PSI-SGKB [doi:10.1038/nchembio0709-456]

NMR screening goes cellular

In vitro NMR-based screening has proven to be a powerful approach for identifying fragments or small molecules that bind to biomolecular targets. In contrast, cell-based screening has the advantage of looking at inhibition in a more physiologically relevant context; however, deconvoluting the target of a cellular screen can be challenging. Xie et al. now take advantage of recent advances in in-cell NMR structure determination to conduct a cellular screen with molecular resolution. The authors overexpressed uniformly ¹⁵N-labeled FKBP along with its unlabeled binding partner, the rapamycin binding domain of mTOR (FRB), in Escherichia coli and detected formation of the weakly interacting complex. Addition of the small molecule rapamycin to these cells resulted in formation of the more tightly binding ternary complex and chemical shift perturbations consistent with the previously characterized rapamycin binding site. Subsequent titration of ascomycin, a natural product that binds FKBP competitively with rapamycin, resulted in displacement of rapamycin from the complex and binding of ascomycin to an overlapping but more extended site on FKBP. Using this system, the authors screened a 289-member dipeptide library and identified peptides that disrupted the FKBP-FRB complex in cells and showed activity in a functional yeast assay. These proof-of-principle results suggest that in-cell NMR will be useful for identifying small-molecule leads and for structurally characterizing small molecule–protein complexes within living cells. ( J. Med. Chem., published online 7 May 2009, doi: 10.1021/jm9000743)

Written by Joanne Kotz