a protein which binds and inhibits phosphorylated proteins, including Nedd4.
ACMA
a fluorescent dye. When ACMA intercalates into a lipid bilayer, it is quenched by a pH gradient across that bilayer.
ASIC
the Acid Sensing Ion Channel family. A well-studied member of the ENaC/DEG superfamily opened by low extracellular pH. In this document, I use ASIC to refer to ASIC1 unless specified.
ASL
airway surface liquid, a layer of mucous which protects the lung.
Acidic Pocket
unfortunately, this name is used to refer to two separate things in the literature. In ASIC, the acidic pocket is between the finger and thumb; the channel opens when the acidic pocket is protonated. In ENaC, the acidic pocket comprises residues from the finger and β-ball and is thought to be involved in sodium self-inhibition.
Aldosterone
a mineralocorticoid hormone essential for regulation of blood pressure and plasma sodium and potassium levels.
Amiloride
a small molecule which blocks ENaC/DEG superfamily ion channels. ENaC binds amiloride several orders of magnitude tighter than other members of the ENaC/DEG superfamily.
Benzamil
a derivative of amiloride with a higher affinity for ENaC.
C2 domain
a lipid- and protein-binding domain.
CCCP
a proton ionophore
CF
cystic fibrosis.
CKO
an ENaC construct with intracellular cysteines knocked out. See Table A.1 for more information.
CKO/DEG
CKO ENaC with additional mutations to bias the channel toward the open state. See Table A.1 for more information.
DDM
n-dodecyl-β-D-maltoside, a detergent commonly used to solubilize membrane proteins.
DM
n-decyl-β-D-maltoside, a detergent commonly used to solubilize membrane proteins.
ECD
the extracellular domain, comprising the palm, knuckle, finger, GRIP, β-ball, and thumb domains.
ENaC
the Epithelial Sodium Channel.
FaNaC
the FMRFamide peptide–activated sodium channel family. A member of the ENaC/DEG superfamily found only in mollusks and gated by a small peptide.
Fab
the antigen-binding portion of an antibody.
GAS belt
a domain swapping loop of TM2 observed in most ASIC structures to date. In ASIC, the GAS belt comprises a Gly-Ala-Ser triad which forms the selectivity filter.
GRIP domain
the Gating Relief of Inhibition by Proteolysis domain. Wedged between the finger and the thumb, when this domain is cleaved by proteases in the α and γ subunits, the channel opens.
HECT domain
the domain of a HECT ligase responsible for transferring a ubiquitin molecule from an E2 ligase to the substrate.
HECT ligase
a family of E3 ligases. Most HECT ligases discussed in this work comprise a C2 domain, a number of WW domains, and a HECT domain.
HG motif
a highly-conserved His-Gly pair which is essential for proper function of ENaC. In ASIC, the HG motif is found in a re-entrant loop which buttresses the GAS belt
I
current. Often used to refer to currents of a specific ion, e.g., INa+ for sodium current.
IC50
concentration of an inhibitor at which the inhibited process is at 50% of its uninhibited value.
Macroscopic current
the current recorded from an entire expression system, e.g., a whole-cell current; cf. unitary current.
N
the number of ion channels at the surface of a cell
NPO
N times PO (the number of channels times their open probability). Essentially the macroscopic current divided by the unitary current.
Nedd4
a family of HECT ligases, including the eponymous Nedd4 and Nedd4-2 (also referred to as Nedd4L)
Open probability
The proportion of time that a given channel spends in the open state.
PHA
pseudohypoaldosteronism. In this text, I discuss only type 1 PHA (PHA1), in which the patient has high plasma potassium and low plasma sodium but normal circulating aldosterone levels.
PIP
phosphatidyl inositol, a phospholipid. Most often found in as a triphosphate (PIP3 or PI3P) or bisphosphate (PIP2 or PI2P).
PY motif
a motif following the form PPXY which is bound by WW domains.
Phenamil
a derivative of amiloride with a higher affinity for ENaC.
PO
see open probability.
SGK
Serum- and glucocorticoid-induced kinase, a serine/threonine kinase with a multitude of roles in cell signaling.
SSI
see sodium self-inhibition.
Sodium self-inhibition
The process by which high extracellular sodium concentrations decrease ENaC currents.
Styrene-Maleic Acid
a copolymer used to directly solubilize a membrane into nanodiscs of native lipids
TM
a transmembrane helix, usually followed by a number (e.g., TM1)
TMD
the transmembrane domain, comprising both TMs from all three subunits (six helices total).
TRC
taste receptor cells. These cells express channels which respond to a single one of the five basic tastes: salty, sweet, sour, bitter, or umami.
Unitary current
currents observed through a single channel; cf. macroscopic current.
Valinomycin
a potassium ionophore
WT
wild-type; a construct which is identical to (or as close as is feasible) to the sequence one would find in the organism.
WW domain
a protein-protein interaction domain. WW domains bind PY motifs.