Cholesteric Proteins

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Abstract
The properties of those proteins (mantis oothecal protein and sea cucumber collagen) which exist in biological systems as cholesteric liquid crystals are reviewed, together with some others (moth and fish eggshell proteins), which it is suspected pass through a cholesteric phase. Indices representing the overall degree of hydrophilicity have been calculated from the amino acid composition of mantis oothecal proteins. These indicate a very high net hydrophilicity which contrasts markedly with the net hydrophobicity of the isotropic oothecal proteins from cockroaches. The high hydrophilicity of mantis oothecins may cause the binding of water and so maintain the liquid crystalline state. Dehydration induced by quinone-tanning could subsequently lead to the solid crystals of the final product. The probable conformation of mantis oothecin is a coiled coil of two α-helices, which meets the requirements of a cholesteric liquid crystalline building block. Functional aspects of cholesteric proteins are discussed.