Table 1.

GdmCl-induced unfolding parameters for the hFXN variants.^a

hFXN	Fluorescence			Circular dichroism
	ΔG°NU H2O	mNU	CmNU	ΔG°UN H2O	mNU	CmNU
90–210	6.7 ± 0.2	2.9	2.3 ± 0.1	6.7 ± 0.2	2.9	2.3 ± 0.1
O-56–210b	6.4 ± 0.1	2.8 ± 0.3	2.3 ± 0.2	6.1 ± 0.8	2.8 ± 0.4	2.2 ± 0.3
m-56–210c	6.5 ± 0.5	2.9 ± 0.3	2.2 ± 0.4	6.3 ± 0.1	2.9 ± 0.4	2.2 ± 0.3

^aA two-state N ↔ U model is assumed. Parameter m_NU is the slope of the linear dependence of free energy of unfolding (ΔG°_NU) on denaturant concentration, and ΔG°_{NU H2O} represents the extrapolated value of ΔG°_NU at zero denaturant concentration. In the fittings corresponding to variant hFXN90–210, we used the predicted m_NU value for GdmCl-induced unfolding, considering a globular protein of identical molecular weight: 2.9 kcal mol⁻¹ M⁻¹ for hFXN90–210. The units of m_NU are kcal mol⁻¹ M⁻¹. C_m and free energy are in M and kcal mol⁻¹, respectively. The parameters for hFXN56–210 were calculated by non-linear least-square fitting of the model to the data shown in Fig. 5, as described in Section 4 and fitting for hFXN90–210 is the same as in Ref. [15].

^bVariant hFXN56–210 expressed in E. coli yields mainly the oligomeric form (O-hFXN56–210). In this case this fraction was purified from E. coli extracts and analyzed.

^cWhen hFXN56–210 is expressed in E. coli, nearly 30% of the recombinant protein remains as soluble monomer (m-hFXN56–210). In this case this fraction was purified and analyzed.