pH gating of ROMK (K _ir 1.1) channels: Control by an Arg-Lys-Arg triad disrupted in antenatal Bartter syndrome

Abstract

Inward-rectifier K ؉ channels of the ROMK (Kir1.1) subtype are responsible for K ؉ secretion and control of NaCl absorption in the kidney. A hallmark of these channels is their gating by intracellular pH in the neutral range. Here we show that a lysine residue close to TM1, identified previously as a structural element required for pH-induced gating, is protonated at neutral pH and that this protonation drives pH gating in ROMK and other K ir channels. Such anomalous titration of this lysine residue (Lys-80 in K ir1.1) is accomplished by the tertiary structure of the Kir protein: two arginines in the distant N and C termini of the same subunit (Arg-41 and Arg-311 in K ir1.1) are located in close spatial proximity to the lysine allowing for electrostatic interactions that shift its pK a into the neutral pH range. Structural disturbance of this triad as a result from a number of point mutations found in patients with antenatal Bartter syndrome shifts the pK a of the lysine residue off the neutral pH range and results in channels permanently inactivated under physiological conditions. Thus, the results provide molecular understanding for normal pH gating of K ir channels as well as for the channel defects found in patients with antenatal Bartter syndrome.

pH sensing in the two-pore domain K + channel, TASK2

“…2 and 3). Therefore, we surmised that several of these residues may collaborate to confer pH sensitivity, as in the case of ROMK1 (21). However, when we combined three of the four K-to-N mutations, each of which individually reduced the pH sensitivity significantly, we had a surprising result: contrary to the expected cumulative effect, leading to almost complete removal of pH sensitivity, the resultant channel (3M) was as sensitive to pH as the WT channel (Fig.…”

Modulation of the Ca2+-Activated Large Conductance K+ Channel by Intracellular pH in Human Renal Proximal Tubule Cells.

“…These data suggest a possibility that pH i -sensitive K ϩ channels usually have the specific pH i -sensitive site in the channel protein. Although the mechanism of pH i -sensitivity in the BK channel of RPTECs is still unknown, our conclusion that H ϩ regulates the activity of this BK channel by binding to the site distinct from Ca 2ϩ sites is supported by findings in the above recent reports [35][36][37]. It is quite likely that H ϩ inhibited the channel activity mainly by the allosteric reduction of the Ca 2ϩ binding affinity.…”

“…On the other hand, a recent report using mSlo3, a member of the BK channel family sensitive to pH i rather than to Ca 2ϩ , provided evidence that the pH i -sensitivity of this channel is independent of Ca 2ϩ -sensitivity [35]. Furthermore, it has also been demonstrated in a cloned pH i -sensitive K ϩ channel, K ir 1.1 (ROMK), that an intracellular lysine close to the M1 segment, composing the pore region, has been identified as the structural element necessary for pH idependent gating [36,37]. These data suggest a possibility that pH i -sensitive K ϩ channels usually have the specific pH i -sensitive site in the channel protein.…”

Protons Trap NR1/NR2B NMDA Receptors in a Nonconducting State

“…The proton inhibition of Kir1.1 is driven by protonation of the amino group of a lysine residue in the intracellular N-terminal domain (corresponds to extracellular N-terminal domain in NMDA receptors) that lies in close proximity to the first transmembrane elements. The pKa of this group is proposed to be influenced by other positively charged residues that are forced into proximity by tertiary structure of the channel complex (Schulte et al, 1999). L-type Ca 2ϩ and cyclic nucleotide-gated channels are similarly controlled by protons, and similar mechanisms have been proposed (Root and MacKinnon, 1994;Chen et al, 1996).…”