Secondary conformational structure of type IV collagen in different conditions determined by Fourier-transform infrared microscopic spectroscopy.

The IR spectra of Type IV collagen in a crystalline state, in a solid film and in aqueous solution were investigated by FT-IR microscopic spectroscopy using either the transmission method or attenuated total reflection method. The effect of compression pressure on the secondary structure of Type IV collagen in different states was also studied. The results indicate that amide I, containing triple helix (1636 cm-1), alpha-helix (1655 cm-1) and random coil (1666 cm-1) peaks, for Type IV collagen in crystalline state had almost the same IR spectral position as that in solid film but the peak areas of amide I, II, III and the proteoglycan region was larger for Type IV collagen in solid film. The IR spectrum of amide I (alpha-helix: 1647 cm-1, triple helix: 1633 cm-1) for Type IV collagen in aqueous solution was different from that in the crystalline state or solid film. The random coil structure existed predominantly in the dry state of collagen. After compression pressure was applied to the crystal of type IV collagen, its IR spectrum transformed significantly. The peak area of amide I was clearly enlarged but the peak area of amide II decreased sharply. When the compression was applied to the solid film, its IR spectral position did not change but both peak areas of amide I and II decreased significantly although the peak area in amide III and the proteoglycan region were almost the same. We also found that two new additional peaks at 1054 and 1023 cm-1 appeared in the proteoglycan region for both of the above compressed samples. Pressure seemed to significantly influence the amide I, II and proteoglycan region, leading to the deformation of collagen.