Determination of the amide I Raman tensor for the antiparallel β‐sheet: application to silkworm and spider silks

The amide I Raman tensor corresponding to the antiparallel β‐sheet structure in proteins has been determined by polarized Raman microspectroscopy of fowl feather rachis using polarized Raman spectra excited in the near‐infrared (785 nm). For a Raman tensor principal axis system ( XYZ ), in which X is perpendicular to the plane of the pleated β‐sheet, Y is in the plane of the sheet and perpendicular to the direction of the polypeptide chain, and Z is parallel to the direction of the polypeptide chain, the principal tensor components (α XX , α YY , α ZZ ) are found to satisfy the following relationships: R 1 ≡ α XX /α ZZ = 0.32 and R 2 ≡ α YY /α ZZ = 3.48. With this Raman tensor determination, we show that semiquantitative estimates of the total antiparallel β‐sheet content in β‐rich proteins can be extracted from polarized Raman intensity measurements on the amide I marker of the β‐sheet occurring near 1664 cm −1 . We demonstrate this approach for the β‐rich silk proteins of the silkworm and spider.