3.A.3.3.9
Proton pumping ATPase, AHA2.  94% identical to AHA1 (3.A.3.3.7); generates the plasma membrane pmf.  Cation-binding pockets have been identified (Ekberg et al. 2010).  The pump has been reconstituted into "nanodiscs" in a functionally monomeric form (Justesen et al. 2013).  Regulated at the post-translation level by cis-acting auto-inhibitory domains, which can be relieved by protein kinase-mediated phosphorylation or binding of specific lipid species such as lysophospholipids (Wielandt et al. 2015).  Pumping is stochastically interrupted by long-lived (~100 seconds) inactive or leaky states. Allosteric regulation by pH gradients modulates the switch between these states but not the pumping or leakage rates (Veshaguri et al. 2016).  They dynamics of the pump have been examined (Guerra and Bondar 2015). AHA2 drives root cell expansion (Hoffmann et al. 2018). This protein is 81% identical to the barley (Hordeum vulgare) HA1 of 956 aas and 10 TMSs. Plasma membrane H⁺-ATPase (HA1 and HA2) activity and/or expression is important for regulating the activity of K⁺ transporters and channels under drought stress conditions (Cai et al. 2019). Herbivore exposure enhances A. nanus tolerance to salt stress by activating the jasmonic acid-signalling pathway, increasing plasma membrane H⁺-ATPase activity, promoting cytosolic Ca²⁺ accumulation, and then restricting K⁺ leakage and reducing Na⁺ accumulation in the cytosol (Chen et al. 2020).  Anionic phospholipids stimulate the proton pumping activity of AHA2 (Paweletz et al. 2023). Plasma membrane H⁺-ATPases play roles in mineral nutrition and crop improvement (Zeng et al. 2024).