Table 1.

Secondary structure prediction for three test proteins

	H	E	S	T	O	Sum	RMS
MBP	0.36	0.16	0.08	0.17	0.24	1.01	0.0149
PDB 1LLS	0.43	0.16	0.09	0.13	0.19	1.00
FKPA	0.41	0.20	0.12	0.8	0.25	1.06	0.0119
PDB 1Q6U	0.35	0.155	0.04	0.15	0.305	1.00
TRX	0.30	0.18	0.11	0.8	0.31	0.98	0.0222
PDB 2TRX	0.26	0.255	0.05	0.24	0.195	1.00

The transmission spectra of the E. coli maltose binding protein, FKPA cis-trans isomerase, and oxidized thioredoxin were recorded both at high (16.5, 10.0, and 10.4 mg/mL, respectively) and low (1.65, 1.0, and 1.04 mg/mL) protein concentrations, respectively. The absorption spectrum of each protein was calculated taking the transmission at low protein concentration as the 100% reference. The spectra were corrected for water distortion, normalized in amplitude, and analyzed with the adapted VARSELEC method selecting the best set of 26 spectra among the 29 present in the FTIR/ATR database (3654 combinations). The results (upper line for each protein) are shown as the fraction of residues in each secondary structure type and compared to the values assessed from the PDB (lower line for each protein, in italics). The names of the PDB files used are indicated in the table under the protein name. The assessed values indicated for thioredoxin are the averages of those reported for the two chains present in the unit cell, for which the helical contents (particularly α-helices and 3-10 helices) are strikingly different. The secondary structure type symbols are H for α-helices, E for extended β-strands, S for bends, T for hydrogen bonded turns, and O for others. “Sum” indicates the sum of the relative contents of all structural types. RMS is the root-mean-square deviation calculated for the best fit.