FIGURE 5.

Secondary structure analysis of E_CT1H_CT as carried out by the chemical shift index protocol. A, the sequence alignment of the T. acidophilum E_CT1 (Ta_E_CT1) and the P. horikoshii E_CT (Ph_E_CT) was performed manually and refined by secondary structure comparison. Note that Ph_E_CT has two α-helices connecting β-strands 1 and 2 that are significantly shorter in Ta_E_CT1. The secondary structure for Ph_E_CT (from the crystal structure; Ref. 11) and Ta_E_CT1 (from the H^α and C^α chemical shift values using the chemical shift index (CSI) protocol as described under “Experimental Procedures”). The overall high degree of secondary structure similarity between the two proteins suggests that Ph_E_CT is a good model for Ta_E_CT1. Furthermore, the retention of secondary structure in Ta_E_CT1 when bound to H_CT, as shown here, indicates that the break up of Ta_E_CT1 dimers by the addition of H_CT (Figs. 3 and 4) is accompanied by a rearrangement of secondary structure elements rather than a change in composition of the same. B, the secondary structure analysis of H_CT indicates α-helix for residues ∼95–108. See supplemental Fig. S4 for absolute deviations of ¹Hα and ¹³Cα chemical shift values from random coil values.