Both Basic and Acidic Amino Acid Residues of IpTx_a Are Involved in Triggering Substate of RyR1

Table 1

Effects of the mutant IpTx_a on 𝑃_{𝑠𝑢𝑏𝑠𝑡𝑎𝑡𝑒} of native RyR1 in SR. 𝑃_{𝑠𝑢𝑏𝑠𝑡𝑎𝑡𝑒,𝑚𝑎𝑥} and 𝐸𝐶₅₀ for 𝑃_{𝑠𝑢𝑏𝑠𝑡𝑎𝑡𝑒,𝑚𝑎𝑥} were calculated using (1) as described in “Section 2.” Values are means ± SE of 3–9 experiments. The average lengths of the substate events were determined at 30 nM concentration. Asterisks indicate significant differences from the wild-type toxin for each parameter (Student t-test, 𝑃<0.05). ND: not determined.

	𝑃substate		Mean duration of substate (s)
	𝑃substate,max	EC50 (nM)
Wild type	0.92 ± 0.06	23.27 ± 2.37	4.56 ± 0.42
K8A	0.97 ± 0.01	5.70 ± 2.86*	ND
T26A	0.98 ± 0.05	9.98 ± 1.92*	3.66 ± 0.40*
D15A	0.91 ± 0.05	21.47 ± 1.92	4.50 ± 0.51
R9A	0.75 ± 0.05*	19.91 ± 3.16	5.86 ± 0.52*
K11A	0.70 ± 0.07*	21.76 ± 3.49	4.35 ± 1.07
D13A	0.62 ± 0.07*	21.72 ± 7.92	2.76 ± 0.25*
K19A	0.43 ± 0.07*	21.84 ± 6.47	1.94 ± 0.43*
R31A	0.40 ± 0.03*	19.24 ± 4.65	3.42 ± 0.27*
D2A	0.38 ± 0.08*	28.63 ± 14.02	2.96 ± 0.60*
R23A	0.32 ± 0.09*	19.54 ± 9.36	2.50 ± 0.26*
R24A	0.26 ± 0.08*	26.03 ± 7.01	1.55 ± 0.94*
E29A	0.19 ± 0.03*	6.07 ± 4.28*	1.75 ± 0.29*
K30A	0.19 ± 0.02*	16.66 ± 2.86*	1.72 ± 0.39*
K20A	0.18 ± 0.05*	18.53 ± 8.17	3.64 ± 0.78*
R33A	0.14 ± 0.03*	16.03 ± 5.65*	1.97 ± 0.19*
K22A	0.12 ± 0.02*	18.49 ± 2.88	3.31 ± 0.15*