PA1b Inhibitor Binding to Subunits c and e of the Vacuolar ATPase Reveals Its Insecticidal Mechanism
|Muench, Stephen P.
Delmas, Agnes F.
Da Silva, Pedro
Harrison, Michael A.
|16-KDA PROTEOLIPID SUBUNIT; Biochemistry & Molecular Biology; BIOINSECTICIDE; GENE; H+-ATPASE; MALARIA PARASITE; MEMBRANE; PROTON PUMPS; RING; SITE; V-ATPASES
|AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
|JOURNAL OF BIOLOGICAL CHEMISTRY
The vacuolar ATPase (V-ATPase) is a 1MDa transmembrane proton pump that operates via a rotary mechanism fuelled by ATP. Essential for eukaryotic cell homeostasis, it plays central roles in bone remodeling and tumor invasiveness, making it a key therapeutic target. Its importance in arthropod physiology also makes it a promising pesticide target. The major challenge in designing lead compounds against the V-ATPase is its ubiquitous nature, such that any therapeutic must be capable of targeting particular isoforms. Here, we have characterized the binding site on the V-ATPase of pea albumin 1b (PA1b), a small cystine knot protein that shows exquisitely selective inhibition of insect V-ATPases. Electron microscopy shows that PA1b binding occurs across a range of equivalent sites on the c ring of the membrane domain. In the presence of Mg.ATP, PA1b localizes to a single site, distant from subunit a, which is predicted to be the interface for other inhibitors. Photoaffinity labeling studies show radiolabeling of subunits c and e. In addition, weevil resistance to PA1b is correlated with bafilomycin resistance, caused by mutation of subunit c. The data indicate a binding site to which both subunits c and e contribute and inhibition that involves locking the c ring rotor to a static subunit e and not subunit a. This has implications for understanding the V-ATPase mechanism and that of inhibitors with therapeutic or pesticidal potential. It also provides the first evidence for the position of subunit e within the complex.
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checked on Mar 3, 2024