6N5W

Crystal structure of the Ca2+/CaM complex with independent peptides of Kv7.4 (KCNQ4) A & B domains

Summary for 6N5W

• Entry DOI: 10.2210/pdb6n5w/pdb
• Descriptor: Potassium voltage-gated channel subfamily KQT member 4, Calmodulin-1, CALCIUM ION, ... (5 entities in total)
• Functional Keywords: ion channel, calmodulin, kcnq4 peptides, complex, metal binding protein
• Biological source: Homo sapiens (Human); More
• Total number of polymer chains: 3
• Total formula weight: 23216.27

Authors

Taylor, A.B.,Archer, C.R.,Shapiro, M.S. (deposition date: 2018-11-22, release date: 2019-03-13, Last modification date: 2023-10-11)

Primary citation

Archer, C.R.,Enslow, B.T.,Taylor, A.B.,De la Rosa, V.,Bhattacharya, A.,Shapiro, M.S.
A mutually induced conformational fit underlies Ca2+-directed interactions between calmodulin and the proximal C terminus of KCNQ4 K+channels.
J. Biol. Chem., 294:6094-6112, 2019

PubMed Abstract: Calmodulin (CaM) conveys intracellular Ca 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] 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/CaM imposed helical structure on both KCNQ A and B domains. Isothermal titration calorimetry revealed that Ca/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/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-free CaM to interact with the KCNQ4 B domain ( ∼10-20 μm), with increasing Ca 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, 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-dependent regulation of KCNQ gating.

PubMed: 30808708
DOI: 10.1074/jbc.RA118.006857

Experimental method

X-RAY DIFFRACTION (2.15 Å)