Table 3.

Comparison of Observed and Predicted Interactions of KGlu or NaGlu with Globular Proteins and KGlu m-values for NTL9 Unfolding

Proteina (Preferential Interaction)	Salt (Concentration)	μ23 (kcal mol−1 m−1)		μ23/ASA (cal mol−1 m−1Å−2)b
		Observed	Predictedc	Observed	Predictedc
Tubulin	NaGlu(1 M)	27.6 ± 3.7d	18.6 ± 4	0.9 ± 0.1	0.6 ± 0.1
BSA	KGlu (0–1 molal)	22.4 ± 2.2e	18 ± 2.7	0.8 ± 0.1	0.6 ± 0.1
	NaGlu (1 M)	35.9 ± 2.3d	18 ± 2.7	1.3 ± 0.1	0.6 ± 0.1
β-lactoglobulin	NaGlu (1 M)	18.9 ± 0.6d	9.3 ± 1.8	1.2 ± 0.1	0.6 ± 0.1
Lysozyme	NaGlu (1 M)	5.7 ± 2.5d	2.7 ± 1.2	0.9 ± 0.4	0.4 ± 0.2
Protein unfolding	salt (concentration)	m-value = Δμ23 (kcal mol−1 m−1)		m-value/ΔASA = Δμ23/ΔASA (cal mol−1 m−1 Å−2)
		Observed	Predicted	Observed	Predicted
NTL9f	KGlu (0–1.5 M)	1.9 ± 0.2	1.4 ± 0.3	1.1 ± 0.1	0.8 ± 0.1

^aTubulin and β-lactoglobulin are dimers; BSA and lysozyme are monomers.

^bPDB files used for ASA calculations (see Table S3) are PDB: 1TUB for tubulin (59); PDB: 4F5S for BSA (60); PDB: 4TLJ for β-lactoglobulin (61); and PDB: 6LYZ for lysozyme (62).

^cPredicted μ₂₃-values are calculated from Eq. 5 using α_i-values from Table 1 and ASA information from Table S3.

^dValues of μ₂₃ for interactions of NaGlu with native proteins at 20°C are calculated from the Donnan coefficient Γ₂₃ ≈ −μ₂₃/μ₃₃ (obtained by dialysis/densimetry (19)) using ${\mu }_{33}^{\text{KGlu}}$ = 1.90 RT/m₃ determined for KGlu in Fig. S1.

^eValue of μ₂₃ for interaction of KGlu with BSA is calculated from Γ₂₃ determined by VPO at 24–25°C (29) using ${\mu }_{33}^{\text{KGlu}}$ = 1.90 RT/m₃.

^fExperimental NTL9 m-value is from Sengupta et al. (20), with an estimated experimental uncertainty of ±10%. Predicted NTL9 m-value and uncertainty are calculated from Eq. 8 using the six α_i-values from Table 1 and estimates of the corresponding ΔASA_i for unfolding NTL9 to the best-fit (compact) model of the denatured state ensemble at 20°C (20).