A mutually induced conformational fit underlies Ca2+-directed interactions between calmodulin and the proximal C terminus of KCNQ4 K+channels.Archer, C.R., Enslow, B.T., Taylor, A.B., De la Rosa, V., Bhattacharya, A., Shapiro, M.S.
(2019) J. Biol. Chem. 294: 6094-6112
- PubMed: 30808708
- DOI: 10.1074/jbc.RA118.006857
- PubMed Abstract:
Calmodulin (CaM) conveys intracellular Ca <sup>2+ </sup> signals to KCNQ (Kv7, "M-type") K <sup>+ </sup> channels and many other ion channels. Whether this "calmodulation" involves a dramatic structural rearrangement or only slight perturbations of t ...
Calmodulin (CaM) conveys intracellular Ca 2+ signals to KCNQ (Kv7, "M-type") K + channels and many other ion channels. Whether this "calmodulation" involves a dramatic structural rearrangement or only slight perturbations of the CaM/KCNQ complex is as yet unclear. A consensus structural model of conformational shifts occurring between low nanomolar and physiologically high intracellular [Ca 2+ ] is still under debate. Here, we used various techniques of biophysical chemical analyses to investigate the interactions between CaM and synthetic peptides corresponding to the A and B domains of the KCNQ4 subtype. We found that in the absence of CaM, the peptides are disordered, whereas Ca 2+ /CaM imposed helical structure on both KCNQ A and B domains. Isothermal titration calorimetry revealed that Ca 2+ /CaM has higher affinity for the B domain than for the A domain of KCNQ2-4 and much higher affinity for the B domain when prebound with the A domain. X-ray crystallography confirmed that these discrete peptides spontaneously form a complex with Ca 2+ /CaM, similar to previous reports of CaM binding KCNQ-AB domains that are linked together. Microscale thermophoresis and heteronuclear single-quantum coherence NMR spectroscopy indicated the C-lobe of Ca 2+ -free CaM to interact with the KCNQ4 B domain ( K d ∼10-20 μm), with increasing Ca 2+ molar ratios shifting the CaM-B domain interactions via only the CaM C-lobe to also include the N-lobe. Our findings suggest that in response to increased Ca 2+ , CaM undergoes lobe switching that imposes a dramatic mutually induced conformational fit to both the proximal C terminus of KCNQ4 channels and CaM, likely underlying Ca 2+ -dependent regulation of KCNQ gating.
Biochemistry and Structural Biology and.,the Long School of Medicine, University of Texas Health San Antonio, San Antonio, Texas 78229.,From the Departments of Cell and Integrative Physiology and email@example.com.,From the Departments of Cell and Integrative Physiology and.