SUMMARY The transduction of transmembrane electric fields into protein motion plays an essential role in the generation and propagation of cellular signals. Voltage-sensing domains (VSD) carry out these functions through reorientations of S4 helix with discrete gating charges. Here, crystal structures of the VSD from Ci-VSP were determined in both, active (Up) and resting (Down) conformations. The S4 undergoes a ~5 Å displacement along its main axis accompanied by a ~60o rotation, consistent with the helix-screw gating mechanism. This movement is stabilized by a change in countercharge partners in helices S1 and S3, generating an estimated net charge transfer of ~1 eo. Gating charges move relative to a “hydrophobic gasket” that electrically divides intra and extracellular compartments. EPR spectroscopy confirms the limited nature of S4 movement in a membrane environment. These results provide an explicit mechanism for voltage sensing and set the basis for electromechanical coupling in voltage-dependent cellular activities.

The accumulation of aggregates of amyloidogenic peptides is associated with numerous human diseases. One well studied example is the association between deposition of amyloid β (Aβ) and Alzheimer's disease. Insulin degrading enzyme and neprilysin are involved in the clearance of Aβ, and presequence peptidase is suggested to play a role in the degradation of mitochondrial Aβ. Recent structural analyses reveal that these three peptidases contain a catalytic chamber (crypt) that selectively encapsulates and cleaves amyloidogenic peptides, hence the name cryptidase. The substrate selectivity of these cryptidases is determined by the size and charge distribution of their crypt as well as the conformational flexibility of substrates. The interaction of Aβ with the catalytic core of these cryptidases is controlled by conformational changes that make the catalytic chambers accessible for Aβ binding. These new structural and biochemical insights into cryptidases provide potential therapeutic strategies for the control of Aβ clearance.

SignificanceIon channels are pore-forming proteins spanning biological membranes. Transient receptor potential ion channels are a subclass of ion channel proteins, characterized by nonselective permeability to cations such as sodium, calcium, magnesium, and zinc, and little voltage sensitivity; their gating is still an area of active investigation. TRPM6 and TRPM7 are ubiquitously expressed with prominent roles in early embryonic development. Uniquely, these channels also include an active kinase domain. The functions of TRPM6 and TRPM7 are correlated with proteolytic cleavage of the kinase domain, which is then translocated to the nucleus to phosphorylate histones and regulate gene expression. Here we describe the structure of the TRPM7 transmembrane regions and compare its features to other ion channels.