Abstract
RCK domains regulate the activity of K+ channels and transporters in eukaryotic and prokaryotic organisms by responding to ions or nucleotides. The mechanisms of RCK activation by Ca2+ in the eukaryotic BK and bacterial MthK K+ channels are well understood. However, the molecular details of activation in nucleotide-dependent RCK domains are not clear. Through a functional and structural analysis of the mechanism of ATP activation in KtrA, a RCK domain from the B. subtilis KtrAB cation channel, we have found that activation by nucleotide requires binding of cations to an intra-dimer interface site in the RCK dimer. In particular, divalent cations are coordinated by the γ-phosphates of bound-ATP, tethering the two subunits and stabilizing the active state conformation. Strikingly, the binding site residues are highly conserved in many different nucleotide-dependent RCK domains, indicating that divalent cations are a general cofactor in the regulatory mechanism of many nucleotide-dependent RCK domains.
Highlights
RCK domains are conserved regulatory domains of K+ channels and transporters (Giraldez and Rothberg, 2017)
The eukaryotic Slo K+ channels are regulated by cation-dependent RCK domains: BK or Slo1 is activated by Ca2+, Slo2 by Na+ and Slo3 is pH-dependent
We have established that the activation mechanism of KtrA, a nucleotide-dependent RCK domain, involves the divalent cations, Ca2+ or Mg2+, as cofactors
Summary
RCK (regulator of conductance of K+) domains are conserved regulatory domains of K+ channels and transporters (Giraldez and Rothberg, 2017). Like in the BK channel, some of the Ca2+ sites are at protein interfaces so that cation binding alters the conformation of the RCK dimeric unit, stabilizing the ring in an activated state and opening the channel (Smith et al, 2012; Smith et al, 2013). KtrAB is a cation channel with a nucleotide-dependent RCK domain This channel is an essential component of the K+ homeostasis machinery in many bacteria, involved in adaptation to osmotic stress and in pH regulation (Holtmann et al, 2003; Ochrombel et al, 2011). We reveal that one of these residues is highly conserved and has a crucial role in cation binding especially, in the chelation of divalent cations This role is essential for the adoption of the active conformation of the RCK domain. We have provided a new understanding of the mechanism of regulation by nucleotides in nucleotide-dependent RCK domains
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
