Psoromic Acid is a Selective and Covalent Rab-Prenylation Inhibitor Targeting Autoinhibited RabGGTase

Abstract

Post-translational attachment of geranylgeranyl isoprenoids to Rab GTPases, the key organizers of intracellular vesicular transport, is essential for their function. Rab geranylgeranyl transferase (RabGGTase) is responsible for prenylation of Rab proteins. Recently, RabGGTase inhibitors have been proposed to be potential therapeutics for treatment of cancer and osteoporosis. However, the development of RabGGTase selective inhibitors is complicated by its structural and functional similarity to other protein prenyltransferases. Herein we report identification of the natural product psoromic acid (PA) that potently and selectively inhibits RabGGTase with an IC50 of 1.3 μM. Structure–activity relationship analysis suggested a minimal structure involving the depsidone core with a 3-hydroxyl and 4-aldehyde motif for binding to RabGGTase. Analysis of the crystal structure of the RabGGTase:PA complex revealed that PA forms largely hydrophobic interactions with the isoprenoid binding site of RabGGTase and that it attaches covalently to the N-terminus of the α subunit. We found that in contrast to other protein prenyltransferases, RabGGTase is autoinhibited through N-terminal αHis2 coordination with the catalytic zinc ion. Mutation of αHis dramatically enhances the reaction rate, indicating that the activity of RabGGTase is likely regulated in vivo. The covalent binding of PA to the N-terminus of the RabGGTase α subunit seems to potentiate its interaction with the active site and explains the selectivity of PA for RabGGTase. Therefore, psoromic acid provides a new starting point for the development of selective RabGGTase inhibitors.

Biomimetic Reagents for the Selective Free Radical and Acid–Base Chemistry of Glycans: Application to Glycan Structure Determination by Mass Spectrometry

“…3 The reaction mixture was stirred at 0 ˚C for 30 minutes and then warmed to room temperature and stirred overnight. The reaction mixture was washed by water and brine, dried over Na 2 SO 4 , filtered, and concentrated in vacuo.…”

“…3 The reaction mixture was stirred under S14 reflux overnight. After cooling to room temperature, the reaction mixture was concentrated in vacuo.…”

mGluR3 Activation Recruits Cytoplasmic TWIK-1 Channels to Membrane that Enhances Ammonium Uptake in Hippocampal Astrocytes

“…The proteins in Rab-GTPase family are critical regulators for vesicle trafficking, including endosomal trafficking, and prenylation of the Rab proteins is required for the newly synthesized Rabs to be delivered to the membranes of donor compartments in vesicle trafficking [36]. Thus, we incubated the brain slices with a selective RabGGTase inhibitor, psoromic acid (PA, 5 μM, 4 h), to prevent covalent Rab-prenylation [37]. This treatment resulted in a significant V M hyperpolarization, −76.29±0.27 mV ( n =14, Fig.…”

“…Selective inhibition of covalent Rab-prenylation by PA also completely eliminated mGluR3-mediated potentiation of on NH 4 + uptake (Fig. 8d); thus, the Rab-associated membrane trafficking is also required for mGluR3 action [37]. …”

Molecular basis of Charcot–Marie–Tooth type 2B disease

“…For Rab proteins, as prenylation is responsible for membrane delivery and it is mediated by a RabGGTase (Rab geranylgeranyltransferase) which covalently attaches two (or, in a few cases, one) geranylgeranyl moieties to cysteine residues at their C-terminus, inhibitors of RabGGTase have been used [48,49].…”