Mapping of Supramolecular Chirality in Insect Wings by Microscopic Vibrational Circular Dichroism Spectroscopy: Heterogeneity in Protein Distribution

The supramolecular chirality of the hindwing of Anomala albopilosa (male) was investigated using a microscopic vibrational circular dichroism (VCD) system, denoted as MultiD-VCD. The source of intense infrared (IR) light for the system was a quantum cascade laser. Two-dimensional maps of IR and VCD spectra were taken by scanning the surface area (ca. 2 mm x 2 mm) of the insect hindwing tissue. The spectra ranged from 1500 to 1700 cm(-1), and the maps have a spatial resolution of 100 mu m. The distribution of proteins, including their supramolecular structures, was analyzed from the location-dependent spectral shape of the VCD bands assigned to amides I and II. The results revealed that the hindwing consists of segregated domains of proteins with different secondary structures: an alpha-helix (in one part of the membrane), a hybrid of alpha-helix and beta-sheet (in another part of the membrane), and a coil (in a vein).