biostudies-literatureArcher CRHHS | National Institutes of HealthUniversity of Texas Health Science Center at San AntonioNCATS NIH HHSMorrison TrustNIAID NIH HHSNHLBI NIH HHSNINDS NIH HHSNCI NIH HHSNIGMS NIH HHSNIH HHS6094-6112https://www.ebi.ac.uk/biostudies/studies/S-EPMC6463706biostudies-literatureUnknown294(15)Calmodulin (CaM) conveys intracellular Ca²⁺ 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 [Ca²⁺] 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 Ca²⁺/CaM imposed helical structure on both KCNQ A and B domains. Isothermal titration calorimetry revealed that Ca²⁺/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 Ca²⁺/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 Ca²⁺-free CaM to interact with the KCNQ4 B domain (<i>K_d</i> ∼10-20 μm), with increasing Ca²⁺ 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 Ca²⁺, 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 Ca²⁺-dependent regulation of KCNQ gating.The Journal of biological chemistryA mutually induced conformational fit underlies Ca²⁺-directed interactions between calmodulin and the proximal C terminus of KCNQ4 K⁺ channels.PMC6463706R01 AI104476UL1 TR001120T32 HL007446P30 GM124165P30 CA054174Research AwardR01 NS043394F31 NS090887K12 GM111726Faculty Scholar AwardS10 OD021527R01 NS065138R01 NS094461R56 NS065138Enslow BTBhattacharya AArcher CRTaylor ABShapiro MSDe la Rosa VfalseA mutually induced conformational fit underlies Ca²⁺-directed interactions between calmodulin and the proximal C terminus of KCNQ4 K⁺ channels.Calmodulin (CaM) conveys intracellular Ca²⁺ 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 [Ca²⁺] 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 Ca²⁺/CaM imposed helical structure on both KCNQ A and B domains. Isothermal titration calorimetry revealed that Ca²⁺/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 Ca²⁺/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 Ca²⁺-free CaM to interact with the KCNQ4 B domain (<i>K_d</i> ∼10-20 μm), with increasing Ca²⁺ 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 Ca²⁺, 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 Ca²⁺-dependent regulation of KCNQ gating.2019-01-01T00:00:00Z2019 Apr2026-04-29T22:54:40.419Z2025-04-04T09:44:08.358ZS-EPMC64637063080870810.1074/jbc.ra118.00685710.1074/jbc.RA118.006857