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

The amide I Raman tensor corresponding to the antiparallel beta-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 beta-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 (alpha(XX), alpha(YY), alpha(ZZ)) are found to satisfy the following relationships: R-1 = alpha(XX)/alpha(ZZ) = 0.32 and R-2 = alpha(YY)/alpha(ZZ) = 3.48. With this Raman tensor determination, we show that semiquantitative estimates of the total antiparallel beta-sheet content in beta-rich proteins can be extracted from polarized Raman intensity measurements on the amide I marker of the beta-sheet occurring near 1664 cm(-1). We demonstrate this approach for the beta-rich silk proteins of the silkworm and spider. Copyright (C) 2006 John Wiley & Sons, Ltd.