Table 1 Model parameters.

Peptide	1a affinity	1b affinity	2a affinity	2b affinity	3 affinity
Sla1 SH3#1	-	-	7.5 ^a	-	7.5 ^a
Sla1 SH3#2	-	-	-	20 ^b	-
Sla1 SH3#3	-	30 ^b	-	-	30 ^b
Cloud SH3	-	-	1	1	-
Ysc84 SH3	2.2 ^a	4.4 ^a	4.4 ^a	4.4 ^a	4.4 ^a
Bzz1 SH3#1				7.5 ^c
Bzz1 SH3#2					7.5 ^c
Actin	-	11.5 ^d	-	3.5 ^d	6.5 ^d
Default values^e
SH3 domain base rates			Actin base rates
k_on (µM⁻¹ s⁻¹)	k_off (s⁻¹)	K_d (µM)	k_on (µM⁻¹ s⁻¹)	k_off (s⁻¹)	K_d (µM)
0.98 × 10⁹	63.7	0.065	7 × 10⁶	0.17	0.024
Other parameter values
Binding radius	Barbed end k_on	Barbed end k_off	Pointed end k_on	Pointed end k_off
7.346 nm^f	11.6 M⁻¹ s⁻¹	1.4 s⁻¹	1.3 M⁻¹ s⁻¹	0.8 s⁻¹
Las17 dimerisation affinity when cooperatively binding actin	Side actin k_on	Side actin k_off	Ysc83-YAB affinity for actin
0.15 µM^g	2.18 M⁻¹ s⁻¹	1.3 × 10³ s⁻¹	0.15 µM

Affinities are in µM. Where the table lists no value, it was modelled as having no interaction. ^aObtained using BLI⁵. ^bCalculated from the model. ^cUses the Sla1-SH3#1 affinity obtained using BLI. ^dMeasured in G-buffer using MST and adjusted. ^eFor each interaction the affinity (K_d) is determined by the ratio between k_on and k_off. If the affinity is stronger than that obtained from default values, k_on is increased and k_off is decreased by the same ratio to give the correct affinity. ^fThis value is the maximum permitted separation for binding to be allowed and is given by \(\:r=\sqrt[3]{\frac{3{k}_{on}\varDelta\:t}{4\pi\:{10}^{3}{N}_{a}}}\:\) where the on-rate k_on is the diffusion-controlled on-rate, assumed to be 10⁸ M⁻¹ s⁻¹²⁴, Δt is the timestep (1 µs), and N_a is Avogadro’s number²⁵. Each individual interaction was then assigned a binding probability P, determined by the on-rate defined for that interaction and listed in Table 1, given by P = 3 k_onΔt/4000πN_ar³, and an unbinding probability given by the timestep multiplied by k_off. ^gTaken from²⁶.

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