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Comparison of K+ and mechano-sensitive ion channels

Comparison of K+ and mechano-sensitive ion channels. Cha et al. Nature 402:813-817. Why compare KcsA and MscS. Voltage gated ion channels are extensively studied by physiological means But the crystal structure is not known X-ray structure of bacterial K+ channel (KcsA) exists

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Comparison of K+ and mechano-sensitive ion channels

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  1. Comparison of K+ and mechano-sensitive ion channels Cha et al. Nature 402:813-817

  2. Why compare KcsA and MscS • Voltage gated ion channels are extensively studied by physiological means • But the crystal structure is not known • X-ray structure of bacterial K+ channel (KcsA) exists • Structure of MscS recently reported. This channel responds to voltage changes • Comparison of these two structures may reveal more about voltage gated K+ channels

  3. KcsA

  4. Consensus Sequence of K+ Channels

  5. MscS

  6. Pore region of KcsA

  7. Charged residues in KcsA • Thr, Tyr and Asp polar residues in the selectivity filter. • Glu51 and Asp80 are found near the selectivity filter. • The four Glu119 residues form a ring of oxygen at the cytoplasmic end.

  8. Polar residues of MscS

  9. Polar residues on TM3 of MscS • Polar residues on TM3 are located at water membrane interface.

  10. Charged residues on MscS • Charges on the loop reside at the water membrane interface. • Arg74 and Arg46 important for voltage sensing. • Arg88 the only charged residue that points into the pore region.

  11. Gating mechanism in KcsA • Fig Residues Ala-92, Val-95 and Met-96 on TM2 are in contact with the small pore helix at Thr72 (purple). • Thr-72 serves as a fulcrum for the rocking motion of TM2. • Such rocking motion in minimal and does not perturb the selectivity filter.

  12. Conclusion • KcsA is predominantly non-polar except for the selectivity filter. The pore region of MscS is non-polar but the rest is very polar. • Basic residues on MscS may be responsible for voltage sensing. • The gating mechanism of MscS is not studied extensively.

  13. Name Residues Conserved residues TM1 29-52 G30, L35, S44, E50 and A51 loop 53-61 G88, Pore helix 62-73 W68, W69, T72 Selectivity filter & loop 74 to 79 selectivity filter 80-84 loop P83 TM2 85-119 G88, V91, A98, G99, L104 and F116 Structural summary of KscA (1BL8)

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