All-Atom Simulations Uncover the Molecular Terms of the NKCC1 Transport Mechanism

The
secondary-active Na–K–Cl cotransporter 1 (NKCC1),
member of the cation–chloride cotransporter (CCC) family, ensures
the electroneutral movement of Cl–, Na+, and K+ ions across cellular membranes. NKCC1 regulates
Cl– homeostasis and cell volume, handling a pivotal
role in transepithelial water transport and neuronal excitability.
Aberrant NKCC1 transport is hence implicated in a variety of human
diseases (hypertension, renal disorders, neuropathies, and cancer).
Building on the newly resolved NKCC1 cryo-EM structure, all-atom enhanced
sampling simulations unprecedentedly unlock the mechanism of NKCC1-mediated
ion transport, assessing the order and the molecular basis of its
interdependent ion translocation. Our outcomes strikingly advance
the understanding of the physiological mechanism of CCCs and disclose
a key role of CCC-conserved asparagine residues, whose side-chain
promiscuity ensures the transport of both negatively and positively
charged ions along the same translocation route. This study sets a
conceptual basis to devise NKCC-selective inhibitors to treat diseases
linked to Cl– dishomeostasis.