AbstractSecretory proteins of Chironomus tentans larvae form insoluble fibers that are spun into threads used to construct underwater feeding and pupation tubes. The physical properties of spun fibers should reflect their protein constituents.The disassembly and reassembly of secretory protein complexes in vitro were studied by solution turbidity, electron microscopy and circular dichroism spectroscopy. Secretory proteins were able to reform complexes with a similar morphology and dichroic spectrum to that of native complexes. These complexes are stabilized by electrostatic and disulfide bonds.cDNA and genomic cloning indicate that spIs, the 1000-kDa secretory proteins, primarily consist of alternating “constant” and “subrepeat” regions. We synthesized and purified synthetic peptides for each region and used circular dichroism and infrared spectroscopy to measure their secondary structure. Constant peptide consists of α-helix and β-turn. Subrepeat peptide consists of poly(Gly) II-type helix and β-turn.We conclude that spIs form the fibrous backbone of a novel biopolymer with alternating α-helices and poly(Gly)II helices punctuated by β-turns. Such fibers may have unique physical properties.
Structural organization of DNA–protein complexes of chromatin studied by vibrational and electronic circular dichroism
