Hexamerins are the most abundant proteins in larval stages of Holometabola insects. In the pupae haemolymph hexamerins constitute up to 50 % of all proteins [1]. Hexamerins evolved from crustacean hemocyanins but lost the ability to bind copper ions and to transport oxygen [2]; instead, they serve as amino acid source during the non-feeding period, when pupae undergo the development toward the adult stage. There is also evidence that hexamerins are able to bind small organic compounds and hormones such as juvenile hormone, which is involved in cuticule formation and humoral immune defence [1]. Tribolium castaneum known as a red flour beetle is a worldwide pest which causes damages of cereals, legumes and dried stored products. It has evolved resistance against a variety of insecticides [3].
Here we present the structure of native Tribolium castaneum hexamerin solved by cryo-electron microscopy. Hexamerin was purified from T. castaneum pupae and vitrified on holey carbon coated copper grids. Data were collected on FEI Titan Krios microscope operated at 300 kV. The final data analysis led to an electrostatic potential map with the resolution of 3.9 Å. Molecular structure was built into this map. Structure of hexamerin provides a basis for further studies of Tribolium life cycle.