. 2020 Sep 11;119(8):1538–1549. doi: 10.1016/j.bpj.2020.08.038

Table 1.

Reactions and Kinetic Parameters for Hsp90 Activation of v-Src Kinase

No.	Reaction	k_f	k_r
1	H90_open + ATP $⇌ H 90_{o p e n}^{A T P}$	6.7 × 10⁻⁴μM⁻¹ s⁻¹	1.45 × 10⁻¹ s⁻¹
2	$H 90_{o p e n}^{A T P} ⇌ H 90_{c l o s e d}^{A T P}$	1.7 × 10⁻² s⁻¹	5 × 10⁻⁵ s⁻¹
3	$H 90_{c l o s e d}^{A T P} ⇌ H 90_{c o m p a c t}^{A D P}$ + Pi	3.3 × 10⁻¹ s⁻¹	9.3 × 10⁻¹⁴μM⁻¹ s⁻¹
4	$H 90_{c o m p a c t}^{A D P} ⇌$ H90_open + ADP	1 s⁻¹	1 × 10⁻¹μM⁻¹ s⁻¹
5	i $⇌$ d	1 s⁻¹	5 × 10² s⁻¹
6	d $⇌$ m	1 × 10⁻¹ s⁻¹	1 × 10⁻¹ s⁻¹
7	m $⇌$ a	6.5 × 10¹ s⁻¹^a	1 s⁻¹
8d	d + H90_open $⇌$ d⋅H90_open	1 μM⁻¹ s⁻¹	5.6 × 10⁻³ s⁻¹^a
8m	m + H90_open $⇌$ m⋅H90_open	1 μM⁻¹ s⁻¹	6.2 × 10⁻¹ s⁻¹^a
9d	$d + H 90_{o p e n}^{A T P} ⇌ d \cdot H 90_{o p e n}^{A T P}$	Same as 8d	Same as 8d
9m	$m + H 90_{o p e n}^{A T P} ⇌ m \cdot H 90_{o p e n}^{A T P}$	Same as 8m	Same as 8m
10d	$d \cdot H 90_{o p e n} + A T P ⇌ d \cdot H 90_{o p e n}^{A T P}$	Same as 1	Same as 1
10m	$m \cdot H 90_{o p e n} + A T P ⇌ m \cdot H 90_{o p e n}^{A T P}$	Same as 1	Same as 1
11d	$d \cdot H 90_{o p e n}^{A T P} ⇌ d \cdot H 90_{c l o s e d}^{A T P}$	3.3 × 10⁻¹ s⁻¹	5.4 × 10⁻³ s⁻¹^a
11m	$m \cdot H 90_{o p e n}^{A T P} ⇌ m \cdot H 90_{c l o s e d}^{A T P}$	Same as 11d	Same as 2
12d	$d \cdot H 90_{c l o s e d}^{A T P} ⇌ d \cdot H 90_{c o m p a c t}^{A D P} + P i$	Same as 3	Same as 3
12m	$m \cdot H 90_{c l o s e d}^{A T P} ⇌ m \cdot H 90_{c o m p a c t}^{A D P} + P i$	Same as 3	Same as 3
13d	$d \cdot H 90_{c o m p a c t}^{A D P} ⇌ d \cdot H 90_{o p e n} + A D P$	Same as 4	1.8 × 10⁻²μM⁻¹ s⁻¹
13m	$m \cdot H 90_{c o m p a c t}^{A D P} ⇌ m \cdot H 90_{o p e n} + A D P$	Same as 4	2.0μM⁻¹ s⁻¹
14	$d \cdot H 90_{c l o s e d}^{A T P} ⇌ m \cdot H 90_{c l o s e d}^{A T P}$	Same as 6	Same as 6
15	C37 + H90_open $⇌$ C37⋅H90_open	1 μM⁻¹ s⁻¹	1.4 s⁻¹
16	C37 + d $⇌$ d⋅C37	1 μM⁻¹ s⁻¹	5.1 × 10⁻³ s⁻¹^a
17	d + C37⋅H90_open $⇌$ d⋅C37⋅H90_open	Same as 16	4.8 × 10⁻⁴ s⁻¹
18a	d⋅C37 + H90_open $⇌$ d⋅C37⋅H90_open	1 μM⁻¹ s⁻¹	1.3 × 10⁻¹ s⁻¹
18n	$d \cdot C 37 + H 90_{o p e n}^{A T P} ⇌ d \cdot C 37 \cdot H 90_{o p e n}^{A T P}$	Same as 18a	2.8 × 10⁻² s⁻¹
19a	$C 37 + d \cdot H 90_{o p e n} ⇌ d \cdot C 37 \cdot H 90_{o p e n}$	2 × 10⁻¹μM⁻¹ s⁻¹	2.4 × 10⁻² s⁻¹^a
19n	$C 37 + d \cdot H 90_{o p e n}^{A T P} ⇌ d \cdot C 37 \cdot H 90_{o p e n}^{A T P}$	1 μM⁻¹ s⁻¹	2.5 × 10⁻² s⁻¹^a
20	$C 37 + d \cdot H 90_{c l o s e d}^{A T P} ⇌ d \cdot C 37 \cdot H 90_{c l o s e d}^{A T P}$	1 × 10⁻¹μM⁻¹ s⁻¹	1 × 10⁻¹ s⁻¹
21	$d \cdot C 37 \cdot H 90_{o p e n} + A T P ⇌ d \cdot C 37 \cdot H 90_{o p e n}^{A T P}$	Same as 1	3 × 10⁻² s⁻¹
22	$d \cdot C 37 \cdot H 90_{o p e n}^{A T P} ⇌ d \cdot C 37 \cdot H 90_{c l o s e d}^{A T P}$	Same as 11d	2.2 × 10⁻¹ s⁻¹

Hsp90 is abbreviated as H90, and Cdc37 as C37. The boldfaced values are fitted to the experimental data of Hsp90-activation of v-Src. The underlined values are uniquely determined from other parameters so that the total free energy changes in any reaction cycle is zero. The kinetic parameters of the Hsp90 cycle (reactions 1–4) are derived from kinetic analysis of nucleotide-driven changes in fluorescence resonance energy transfer in labeled Hsp90 (28), with the k_f of reaction 1 adjusted by a factor of 2 so that the ATPase has a K_m of 250 μM (11). The kinetic parameters for v-Src conformational transitions—experimentally unavailable—are chosen arbitrarily, except for k_f of reaction 7. The k_f of reactions 11d and 11m reflects a 20-fold acceleration of the closing of the Hsp90 dimer induced by the client (36,37). Other than this acceleration, the client is assumed not to affect the kinetics of other steps of the ATP-driven cycle (reactions 8–13). I also assume that the rates of client’s conformational transition are the same in the closed Hsp90 dimer (reaction 14) as in the solution (reaction 6). All protein-protein association rate constants are taken to be 1 μM⁻¹ s⁻¹, a reasonable value, except for reactions 19a and 20, which should be slower because Cdc37 has to adopt a specific conformation to simultaneously bind to both Hsp90 and the client. The dissociation rate constant of Cdc37 from Hsp90 (reaction 15) is computed from its binding constant K_D = 1.4 μM (49,50). The dissociation rate constant of reaction 20 is arbitrary because the model predictions are insensitive to its value.

Values are fitted to the experimental data of Hsp90 activation of v-Src.