Heat stability of proteins in desiccation tolerant cattail pollen (Typha latifolia): A Fourier transform infrared spectroscopic study.

Secondary structure and aggregation behavior of proteins, as determined in situ in Typha latifolia pollen, were studied by means of Fourier transform infrared microspectroscopy. The amide-I band, arising from the peptide backbone, was recorded over a temperature range from -50 to 120°C at different hydration levels of the pollen. Dehydration increased the denaturation temperature of the proteins and decreased the extent of protein structural rearrangements due to heating. Below 0.16 g H2O/g dry weight (DW), the temperature at which the proteins began to denature increased rapidly. In fully hydrated pollen, denaturation commenced above 60°C, whereas in very dry pollen (0.01 g H2O/g DW) it did at approximately 116°C. Temperature-induced aggregation of proteins was accompanied by the appearance of an infrared band in the region between 1625 and 1630 cm-1 and a weak band around 1692 cm-1. These bands are characteristic of intermolecular extended β-sheet structures. The α-helical band position (band around 1657 cm-1) did not shift substantially over a temperature range from -40 to 120°C at all the water contents tested, indicating that α-helical structures are particularly heat stable. We show here that the proteins in dry desiccation-tolerant pollen are particularly heat stable.