FT-IR Analysis of Jojoba Protein Conformations in D2O

Abstract

FT-IR methods in the literature for determining the secondary structure of proteins in D2O solution involve a curve-fitting step which is somewhat subjective. In an effort to reduce the subjectivity of curve-fitting of protein amide carbonyl absorbances, initial estimations of peak heights and widths were used which were independent of operator judgment. Other restrictions on the curve-fitting procedure were imposed so that different operators would arrive at values for secondary structure consistent with each other and with the literature for papain, hemoglobin, ribonuclease, myoglobin, and alpha-chymotrypsin. This goal was partially achieved by the preliminary method described in this paper. The method was then applied to jojoba proteins and a jojoba protein isolate, the 2S fraction. The jojoba 2S fraction is predominantly beta-structure (51%) and retains its beta-structure in pD 13 solution or at neutral pD when its disulfide linkages are reduced and alkylated. However, dissolving the reduced alkylated protein in pD 13 solution gives a totally random structure by infrared analysis.