The SARS-CoV-2 envelope (E) protein forms a calcium- and voltage-activated calcium channel

Abstract

The function of ion channels is essential in the infectious cycle of many viruses. To facilitate viral uptake, maturation and export, viruses must modify the ionic balance of their host cells, in particular of calcium ions (Ca2+). Viroporins encoded in the viral genome play a key part in altering the cell's ionic homeostasis. In SARS-Coronavirus-2 (SARS-CoV-2) - the causative agent of Covid-19 - the envelope (E) protein is considered to form ion channels in ERGIC organellar membranes, whose function is closely linked to disease progression and lethality. Deletion, blockade, or loss-of-function mutation of coronaviral E proteins results in propagation-deficient or attenuated virus variants. The exact physiological function of the E protein, however, is not sufficiently understood. Since one of the key features of the ER is its function as a Ca2+ storage compartment, we investigated the activity of E in the context of this cation. Molecular dynamics simulations and voltage-clamp electrophysiological measurements show that E exhibits ion channel activity that is regulated by increased luminal Ca2+ concentration, membrane voltage, post-translational protein modification, and negatively charged ERGIC lipids. Particularly, calcium ions bind to a distinct region at the ER-luminal channel entrance, where they activate the channel and maintain the pore in an open state. Also, alongside monovalent ions, the E protein is highly permeable to Ca2+. Our results suggest that the physiological role of the E protein is the release of Ca2+ from the ER, and that the distinct Ca2+ activation site may serve as a promising target for channel blockers, potentially inhibiting the infectious cycle of coronaviruses.

A cooperative knock-on mechanism underpins Ca2+-selective cation permeation in TRPV channels

“…This model correctly replicated experimental values for the hydration-free energy and the number of coordinated water molecules in the first solvation shell and showed Ca 2+ –protein binding energies comparable to the quantum mechanical and polarizable models. The multisite Ca 2+ model has previously been used to investigate ion permeation of Ca 2+ in a range of channels, including the type-1 ryanodine receptor ( Zhang et al, 2020 ; Liu et al, 2021 ), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors ( Schackert et al, 2022 ), and recently the E protein of SARS-CoV-2 ( Antonides et al, 2022 Preprint ).…”

Differential beta‐coronavirus infection dynamics in human bronchial epithelial organoids

“…HCoV‐OC43 upregulated genes associated with the unfolded protein response pathway (V1), a known defense mechanism against CoVs and the modulation of IFNα pathways ( p < 0.05; Figure 5E,F and Supporting Information S1: Figure , Table ), 45 but downregulated genes related to cellular organization and secretory trafficking (V2), potentially impacting viral dissemination ( p < 0.01) 46 . SARS‐CoV and SARS‐CoV‐2 infections were linked to oxidative phosphorylation (V3) 47 and cellular calcium ion homeostasis (V7), 48 respectively, ( p < 0.05). Notably, SARS‐CoV downregulated interferon‐related transcription genes (V4), 49 while SARS‐CoV‐2 affected autophagy response genes (V8) ( p < 0.01) 50 .…”

“…These results suggest that beta‐CoVs can modulate host cellular machinery in various ways, possibly to enhance viral proliferation or evade host immune responses. For example, SARS‐CoV and SARS‐CoV‐2 infections appear to activate pathways that enhance viral proliferation, such as oxidative phosphorylation 47 and the calcium ion pathway, 48 while suppressing the expression of genes related to host cellular transcription and protein synthesis/trafficking. This disruption of host cell functions, particularly prominent in SARS‐CoV‐2‐infected ciliated cells, has been known to suppress host interferon responses 44 .…”

A hydrophobic funnel governs monovalent cation selectivity in the ion channel TRPM5

“…In the case of simulations containing Ca 2+ , the standard CHARMM36m Ca 2+ ions were then replaced with the multi-site Ca 2+ of Zhang et al Zhang et al ( 2020 ). This multi-site model has used been used to investigate Ca 2+ permeation in a number of channels, including including the type-1 ryanodine receptor Zhang et al ( 2020 ); Liu et al ( 2021 ), AMPA receptors Schackert et al ( 2022 ), the E protein of SARS-CoV-2 Antonides et al ( 2022 ), and TRPV channels Ives et al ( 2022 ); Liu and Song ( 2022 ).…”