Table 2.
Thermal unfolding and sedimentation analysis of trpzip peptides
Parameter | trpzip1 | trpzip2 | trpzip3 | trpzip4 | trpzip5 | trpzip6 |
---|---|---|---|---|---|---|
Tm, K | 323.0 ± 0.3 | 345.0 ± 0.1 | 351.8 ± 0.2 | 343.1 ± 0.1 | 315.8 ± 0.2 | 317.7 ± 0.5 |
ΔHm, cal⋅mol−1 | 10,790 ± 120 | 16,770 ± 60 | 13,020 ± 70 | 21,860 ± 60 | 13,320 ± 140 | 10,290 ± 300 |
ΔSm, cal⋅mol−1⋅K−1 | 33.4 | 48.6 | 37.0 | 63.7 | 42.2 | 32.4 |
ΔCp, cal⋅mol−1⋅K−1 | 231 ± 4 | 281 ± 2 | 195 ± 2 | 380 ± 4 | 325 ± 10 | 236 ± 17 |
σobs/σcalc | 1.02 ± 0.04 | 1.01 ± 0.04 | 1.00 ± 0.04 | n. d. | n. d. | n. d. |
Thermal melts were acquired with 20 μM peptide samples in 20 mM potassium phosphate, pH 7.0. σ ≡ reduced apparent molecular weight, as determined from sedimentation data fit to a nonideal single-species model (see Materials and Methods). n.d. ≡ not determined; the thermal denaturation curve of trpzip4 was identical at 5-fold higher peptide concentration (100 μM vs. 20 μM). Thermal unfolding parameters of ΔH = 11,600 cal⋅mol−1 and ΔS = 39 cal⋅mol−1⋅K−1 have been reported for the gb1 peptide, assuming ΔCp = 0 (7; see also Materials and Methods).