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

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

KcsA

Consensus Sequence of K+ Channels

MscS

Pore region of KcsA

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.

Polar residues of MscS

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

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.

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.

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.

Structural summary of KscA (1BL8) NameResiduesConserved residues TM129-52G30, L35, S44, E50 and A51 loop53-61G88, Pore helix62-73 W68, W69, T72 Selectivity filter & loop 74 to 79 selectivity filter loop P83 TM G88, V91, A98, G99, L104 and F116