Table 3. Isothermal titration calorimetry demonstrates that only one molecule of (dT)₃₅ can bind with SSB variants that have two of the four OB folds mutated to block ssDNA binding.

Protein	[NaCl] (mM)	Model	n(1,2) Sites	K(1,2) M−1	ΔH(1,2) kcal mol−1
wtSSB	2	One Site	0.99 ± 0.01	≥1010	(−65.7 ± 0.1)
wtSSB	300	Two Sites	1†	≥1010	(−60.7 ± 0.5)
			2†	(1.30 ± 0.19) × 108	(−63.9 ± 0.7)
SSB LD	2	One Site	0.95 ± 0.01	≥1010	(−63.3 ± 0.1)
SSB LD	300	Two Sites	1†	≥109	(−59.6 ± 0.7)
			2†	(2.0 ± 0.5) × 106	(−43.4 ± 0.4)
SSB LD (αΔW)	2	One Site	0.86 ± 0.01	≥1010	(−56.2 ± 0.2)
SSB LD (αΔW)	300	One Site	0.93 ± 0.01	(2.36 ± 0.10) × 108	(−48.8 ± 0.1)
SSB LD (αΔW F)	2	One Site	0.83 ± 0.01	(1.6 ± 0.3) × 109	(−56.2 ± 0.3)
SSB LD (αΔW F)	300	One Site	0.85 ± 0.01	(8.7 ± 0.5) × 107	(−52.0 ± 0.2)

^†Indicates values that were fixed during model fitting.

These experiments were performed in buffer T at 25.0°C with 20.3–29.3 μM (dT)₃₅ into 0.93–1.86 μM 4-OB of protein. The curves and fits for SSB, SSB LD, SSB LD (αΔW) and SSB LD (αΔW F) are shown in Figure 3C and D.