KCNQ2: Molecular relation to benign familial neonatal convulsion (BFNC)

1. KCNQ2: Molecular relation to benign familial neonatal convulsion (BFNC) Kristian Adams, Daniel Nixon, Josefine Pedersen & Calvin Leung

2. Today… • Topography • M Current • Mutation – R214W • Benign Familial Neonatal Convulsion (BFNC)

3. KCNQ2 – Background Information • Chromosome 20q13.3 • Base pair 62,037,541 to base pair 62,103,992 • Codes for Kv7.2 - – Potassium voltage gated • 872 amino acids in length • Widely expressed in PNS and CNS CCCTAACAGAGTCTTGGGGAGAGCCCCTACCCCCATCCCTTCCCGGAGGCGTCCACTCCCAGGGCCCAGCTGAGAAGACTCCAGTCCTGCTCAGGCGGCTGGGCACCGCTCTGGGACCCCAGGAGCGCTGGGGCCACCAGGCAGGTCCACTTGGTTAGTACTACCGGACTCAAAGGTGACCGCAGGGTCAGTGTGCACATGGCCGGGGGATTGGGCAGGCTCAGCCCAGAGCTCTGGTCCCGCGGGCCTTGGTCCCTTCTGCCTCCCCCTCCTCTCCCCCTGCCCTCCCCTCCCCCTCCCCCACTCCCCCTCCTCTCCCCCTCCCCTCCCCCTCCACTCCTGTCTCCCCCCTCCACTCCTGTCTCCCCTCTCCCCGTCCCCGCCACTCTCCTCCCCTCCCATTCCCCTCTCCTCCCCTCCCCCTCCCTCCTGTCTCCCCTCTCCCCGTCCCCTCTCCCTCCCCTCCCCTCCCTTTCCCTCTTCTCTCCTCCCCTCTCCTCTCCTTCCCCCCTCCCCTCCCCTCCCCGTCCCTCCCTCTCCCCTCCCTTCCCCTCCCTCTCTTCTCCTCCCCTCTCCTTCGACTGGCGTCGCGGGGGTTAACGCGGGGCGGGGCGAGGCGGCGGGCGGAGCCGGCGCGGCCGCGGGCCAGGCGCCGAGGTGCGCGCGGAGCGAGGTGGCCGCAGCGTCTCCGCGCGCGGCCCAAGCCCGGCAGGAGTGCGGAACCGCCGCCTCGGCCATGCGGCTCCGGCCGGGGGGCCTGGGCTGGGGCCCGCGCCGCCCCCCGCGCTCCGCCCCCGCTGAGCCTGAGCCCGACCCGGGGCGCCTCCCGCCAGGCACCATGGTGCAGAAGTCGCAACGGCGGCGTATACCCCGGCCCGAGCGGGGAGAAGAAGCTGAAGGTGGGCTT

4. Kv7.2 Topography

5. Kv7.2 Structure

6. NORMAL FUNCTION OF THE M CHANNEL

7. Co-assembly of subunits in the M-Channel Quaternary structure of the M-Channel. One subunit has been omitted to reveal the channel pore. (Cooper and Jan, 2003)

8. Subunits giving rise to the M-Current (A) Currents recorded in Xenopusoocytes after injection of KCNQ2 mRNA, KCNQ3 mRNA, or KCNQ2 and KCNQ3 mRNA. Currents generated by 2-s voltage steps from a holding potential of −70 mV over the range −60 to 0 mV in 10-mV increments. (B) Histogram displaying the average current response to a voltage-clamp step to 0 mV from −70 mV in cells injected with KCNQ2, KCNQ3, or KCNQ2 and KCNQ3 mRNA (Wang et al, 1998).

9. The M-Current (Delmas & Brown, 2005)

10. Modulation of the M-Current Image source - Courtesy of Dr. Trevor Lewis.

11. Cellular location of the M-Channel

12. R214W Mutations of KCNQ2

13. Topography of the Kv7.2 subunit (Cooper and Jan, 2003)

14. R214W Current traces from Xenopus oocytes expressing homomeric channels in response to a family of voltage steps from -80 to +40 mV in 10 mV increments. Scale - 200 nA, 500 ms. Current traces from heteromeric channels expressed in Xenopus oocytes in response to a family of voltage steps from -80 to +40 mV in 10 mV increments. Scale - 100 nA, 500 msec. (Castaldo et al, 2002)

15. Activation/Deactivation Kinetics (Castaldo et al, 2002)

16. Changes in Voltage Dependence Voltage dependence of conductance of homomeric (left) and heteromeric (right) M-Channels. (Castaldo et al, 2002)

17. Maximal Current of Normal/Mutants (Castaldo et al, 2002)

18. Surface Expression of Normal/Mutant

19. BENIGN FAMILIAL NEONATAL CONVULSIONS

20. Benign familialneonatal convulsions • Rare autosomal-dominant disorder • Mutation in KCNQ2 subunit

21. Symptoms • Focal or generalised tonic-clonic seizures • Unconsciousness, convulsions, and muscle rigidity • Infants - day 3 • 4 weeks

22. Symptoms • Normal neurocognitive development • Spontaneous remission - 12 month • Rare – intellectual disabilities • 10-15% epileptic seizures in adult life • Rare – myokymia • Involuntary and spontaneous contraction of skeletal muscles • Genetic and environmental factors

23. Diagnosis • Electroencephalography (EEG) • Electric activity of the brain • Computedtomography (CT scan) • X-ray • Identification of abnormalities(tumor, strokes, scartissue etc.) • Magneticresonanceimaging (MRI) • Abnormalites

24. Treatment • Drugs – hyperpolarise neurons in CNS • Phenobarbital • Anti-epileptic drug • Allosteric binding to GABAA receptors causes influx of Cl-

25. Summary – R214W • Substitution of the positive arginine residue (R214) with tryptophan (W) in the voltage-sensing S4 domain. • Both homomeric and heteromeric mutant channels exhibit delayed activation, accelerated deactivation, and decreased voltage sensitivity in response to depolarising stimuli. • However, the maximal current and surface expression remain unchanged, unlike other mutations that occur at the pore loop or at the C-terminus of KCNQ2. • Therefore, the M-current becomes more difficult to invoke in neurons that express these mutant channels. • As a result, neuronal excitability increases, leading to the development of BFNC.

26. References • Delmas & Brown (2005).Nature Reviews Neuroscience 6, 850-862. • Cooper, E.C. & Jan, L.Y. (2003). M-channels: neurological diseases, neuromodulation, and drug development. Arch Neurol. 60(4), 496-500. • Wang, H. S., Pan, Z., Shi, W., Brown, B. S., Wymore, R. S., Cohen, I. S., Dixon, J. E. & McKinnon, D. (1998). KCNQ2 and KCNQ3 potassium channel subunits: molecular correlates of the M-channel. Science. 282, 1890–1893. • Cooper EC, Jan LY. (2003) M-channels: Neurological Diseases, Neuromodulation, and Drug Development. Arch Neurol 60, 496-500 • Dedek, K., Kunath, B., Kananura, C., Reuner, U., Jentsch, T. J., Steinlein, O., K. (2001). Myokymia and neonatal epilepsy caused by a mutation in the voltage sensor of the KCNQ2K+ channel. PNAS, 98(21), p. 12272-12277 • Steinlein OK, Conrad C, Weidner B. (2006) Benign familial neonatal convulsions: Always benign? Epilepsy Research, 73(3), 245-249 • Volkers L, Rook MB, Das JHG, Verbeek NE, Groenewegen WA, van Kempen MJA, Lindhout D, Koeleman BPC. (2009) Functional analysis of novel KCNQ2 mutations found in patients with Benign Familial Neonatal Convulsions. Neuroscience Letters, 462(1), 24-29 • Castaldo P, Miraglia del Giudice E, Coppola G, Pascotto A, Annunziato L, Taglialatela M. (2002) Benign familial neonatal convulsions caused by altered gating of KCNQ2/KCNQ3 potassium channels. Journal of Neuroscience, 22, 1-6. • Kwan P, Brodie MJ. (2004) Phenobarbital for the Treatment of Epilepsy in the 21st Century: A Critical Review. Epilepsia, 45(9), 1141-1149.

27. Dynamics of K+ Movement Source: Khalili-Araghi, Tajkhorshid & Schulten, 2006

28. R214W