Rab geranylgeranyl transferase (RabGGTase) catalyzes the attachment of geranylgeranyl isoprenoids to Rab guanine triphosphatases, which are key regulators in vesicular transport. Because geranylgeranylation is required for proper function and overexpression of Rabs has been observed in various cancers, RabGGTase may be a target for novel therapeutics. The development of selective inhibitors is, however, difficult because two related enzymes involved in other cellular processes exist in eukaryotes and because RabGGTase recognizes protein substrates indirectly, resulting in relaxed specificity. We report the synthesis of a peptidic library based on the farnesyl transferase inhibitor pepticinnamin E. Of 469 compounds investigated, several were identified as selective for RabGGTase with low micromolar IC(50) values. The compounds were not generally cytotoxic and inhibited Rab isoprenylation in COS-7 cells. Crystal structure analysis revealed that selective inhibitors interact with a tunnel unique to RabGGTase, implying that this structural motif is an attractive target for improved RabGGTase inhibitors.
Stopping the transfer: Based on the structure of pepticinnamin E, specific inhibitors of Rab geranylgeranyl transferase (RabGGTase) with activity in cells were developed, and the first crystal structure of the enzyme in complex with an inhibitor is reported (see inhibitor structure and positioning in the active site of the enzyme). The findings may have implications for the chemical‐biological study of Rab prenylation and vesicular transport and the involvement of RabGGTase in the establishment of disease.
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