Identification, recombinant production and structural characterization of four silk proteins from the Asiatic honeybee Apis cerana

Unlike silkworm and spider silks assembled from very large and repetitive fibrous proteins, the bee and ant silks were recently demonstrated to consist of four small and non-repetitive colied-coli proteins. The design principle for this silk family remains largely unknown and so far no structural study is available on them in solution. The present study aimed to identify, express and characterize the Asiatic honeybee silk proteins using DLS, CD and NMR spectroscopy. Consequently, (1) four silk proteins are identified, with similar to 6,10, 9 and 8% variations, respectively, from their European honeybee homologs. Strikingly, their recombinant forms can be produced in Escherichia coli with yields of 10-60 mg/l. (2) Despite containing similar to 65% colied-coli sequences, four proteins have very low alpha-helix (9-27%) but unusually high random coli (45-56%) contents. Surprisingly, beta-sheet is also detected in four silk proteins (26-35%), implying the possible presence of beta-sheet in the bee and ant silks. (3) Four proteins lacking of the tight tertiary packing appear capable of interacting with each other weakly but this interaction triggers no significant formation of the tight tertiary packing. The study not only implies the promising potential to produce recombinant honeybee silk proteins for the development of various biomaterials; but also provides the first structural insight into the molecular mechanism underlying the formation of the colied-coli silks. (c) 2008 Elsevier Ltd. All rights reserved.