The voltage-gated proton channel Hv1 is highly selective for H+ and is activated by membrane depolarization and pH gradient. An increased external and decreased internal pH opens the Hv1 channel. The intracellular C-terminal domain of Hv1 is responsible for channel dimerization, cooperative, and thermosensitive gating. Here, we found that proton pump inhibitors (PPIs) interact with the C-terminal domain of human Hv1. The interaction between PPIs and the C-terminal domain, which is pH-dependent, lowered the thermal and structural stability of the protein at pH 4, but enhanced the thermal and structural stability at pH 8. Furthermore, we investigated in vitro the interaction of PPIs with the C-terminal domain of Hv1 by fluorescence and micro-Raman spectra. Fluorescence quenching measurements revealed that the interaction between the C-terminal domain and PPIs is a mainly hydrophobic interaction. The micro-Raman spectra showed that PPIs did not form stable disulfide bonds with the unique thiol group within this domain (Cys249 residue). The preferential interaction of PPIs with the inactive form of Hv1 stabilizes the high pH inactive state of the C-terminal domain, indicating a mechanism by which PPIs might act explicitly on the stabilization of a closed state of the proton channel.

The voltage-gated proton channel Hv1 is strongly sensitive to Zn(2+). The H(+) conduction is decreased at a high concentration of Zn(2+) and Hv1 channel closing is slowed by the internal application of Zn(2+). Although the recent studies demonstrated that Zn(2+) interacts with the intracellular C-terminal domain, the binding sites and details of the interaction remain unknown. Here, we studied the pH-dependent structural stability of the intracellular C-terminal domain of human Hv1 and showed that Zn(2+) binds to His(244) and His(266) residues. The thermodynamics signature of Zn(2+) binding to the two sites was investigated by isothermal titration calorimetry. The binding of Zn(2+) to His(244) (mutant H266A) and His(266) (mutant H244A) were an endothermic heat reaction and an exothermic heat reaction, respectively.

Escherichia coli ATP synthase (F0F1) couples catalysis and proton transport through subunit rotation. The ϵ subunit, an endogenous inhibitor, lowers F1-ATPase activity by decreasing the rotation speed and extending the duration of the inhibited state (Sekiya, M., Hosokawa, H., Nakanishi-Matsui, M., Al-Shawi, M. K., Nakamoto, R. K., and Futai, M. (2010) Single molecule behavior of inhibited and active states of Escherichia coli ATP synthase F1 rotation. J. Biol. Chem. 285, 42058-42067). In this study, we constructed a series of ϵ subunits truncated successively from the carboxyl-terminal domain (helix 1/loop 2/helix 2) and examined their effects on rotational catalysis (ATPase activity, average rotation rate, and duration of inhibited state). As expected, the ϵ subunit lacking helix 2 caused about ½-fold reduced inhibition, and that without loop 2/helix 2 or helix 1/loop 2/helix 2 showed a further reduced effect. Substitution of ϵSer(108) in loop 2 and ϵTyr(114) in helix 2, which possibly interact with the β and γ subunits, respectively, decreased the inhibitory effect. These results suggest that the carboxyl-terminal domain of the ϵ subunit plays a pivotal role in the inhibition of F1 rotation through interaction with other subunits.

The Eighth International Biennial Conference on RNA polymerases I and III (the \'Odd Pols\') was held June 7-11, 2012 at The Airlie Center in Warrenton Virginia, USA. It was sponsored by the Universite Laval and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, and organized by Rich Maraia and Tom Moss. The meeting honored the memory of Pierre Thuriaux (Jan 1, 1950-March 18, 2012) and David Schneider reminisced on the important accomplishments his mentor Masayasu Nomura (1927-2011). The goal of the conference was to bring together the world\'s experts on RNA polymerase I and RNA polymerase III to highlight and share their latest results and varied experimental approaches. The meeting drew attendees from twelve countries and most contributed through oral and poster presentations. The talks were organized into several sessions subdivided into 10 distinct topics. The keynote speaker, Ian Willis, opened the meeting with his presentation entitled \"New Regulators of Signaling to Odd Pols\" and the closing presentation was given by Patrick Cramer with his presentation \"Conservation of the RNA polymerase I, II and III transcription initiation machineries\". Here we present some of the highlights from the meeting using summaries provided by the participants.