Fig. 5.

The BK inner pore is much broader than that of many other K⁺ channels. (A) Estimation of the minimal radius of BK pore at positions that allow two independent modifications by MTSET, A313C and S317A, based on the size of MTSET (3 Å in radius, blue sphere) and hydrated K⁺ (3 Å in radius, purple sphere). (B) Radius profiles of various K⁺ channels were calculated from their crystal structures by using the program HOLE (43). The horizontal dotted lines mark the levels of Shaker I470 (red) and V474 (black), respectively. The vertical lines mark the minimal radius of 7.3 Å at the level of 313 or 317 in the BK inner pore.