Issues

In this issue, Michelucci et al. report the existence of specific sites acting as Ca²⁺ entry units (CEUs) in fast skeletal muscle of mice lacking calsequestrin (CASQ1), the major Ca²⁺ binding protein of the SR. The CEU provides constitutive and store-operated Ca²⁺ entry (SOCE) and resistance to force decline resulting from SR Ca²⁺ depletion during repetitive muscle activity.

Cherny and coworkers use zinc ion as a probe to identify different conformational states of voltage-gated proton (Hv1) channels.

Agonist actions at transition states can explain the observation that different pathways are taken for acetylcholine receptor desensitization and recovery.

Mice lacking calsequestrin-1 have reduced levels of releasable Ca²⁺ in the sarcoplasmic reticulum of their skeletal muscles. Michelucci et al. reveal that this is compensated by constitutive assembly of STIM1 and Orai1 into Ca²⁺ entry units, promoting both constitutive and store-operated Ca²⁺ entry.

The voltage-gated proton channel (H_V1) resembles the voltage sensors of other channels, but its movement during channel opening remains controversial. Cherny et al. establish open and closed gating configurations of H_V1 by analyzing the interactions of Zn²⁺ with an introduced histidine residue.

Stress increases the permeability of the mitochondrial inner membrane by activating permeability transition pores (PTPs), likely composed of ATP synthase or the adenine nucleotide translocator. By measuring water flux during calcium-activated mitochondrial swelling, Neginskaya et al. estimate that if these proteins are involved in PTP, only a small fraction becomes transformed into the pore on a single mitochondrion.

K⁺ binding to mammalian glutamate transporters is essential for the import and release of glutamate into cells. Using MD simulations and site-directed mutagenesis, Wang et al. identify two K⁺ binding sites in the transporter EAAC1, one of which appears to catalyze the relocation step of the transport cycle.