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Figure 2
Purification and characterization of Tako8 and Ika proteins. The SDS–PAGE confirmed the purity of the proteins (a). In all figures, Tako8, Ika8, Ika4 and Ika2 are represented by blue, green, orange and red lines, respectively. The analytical SEC (b) and AUC (c) show that the proteins are monodisperse, with the expected mass. The UV CD spectra indicate β-structure (d) which can be used to observe thermal denaturation (e). The resistance of the protein towards denaturation by GdnHCl was monitored using tryptophan fluorescence. Fractional denaturation was determined from the ratio of emission at 350 and 330 nm after excitation at 280 nm (f). Both temperature and chemical denaturation indicate that the Ika proteins are more stable than Tako8 and that the Ika proteins increase in stability with polypeptide length. All proteins were dissolved in 20 mM phosphate buffer pH 7.6 (no NaCl) for folding and stability experiments (d, e, f).

IUCrJ
Volume 6| Part 1| January 2019| Pages 46-55
ISSN: 2052-2525
https://doi.org/10.1107/S205225251801480X