Amyloids protect the silkmoth oocyte and embryo

Abstract

Chorion is the major component of silkmoth eggshell. More than 95% of its dry mass consists of proteins that have remarkable mechanical and chemical properties protecting the oocyte and the developing embryo from a wide range of environmental hazards. We present data from electron microscopy (negative staining and shadowing), X-ray diffraction and modeling studies of synthetic peptide analogues of silkmoth chorion proteins indicating that chorion is a natural amyloid. The folding and self-assembly models of chorion peptides strongly support the L L-sheet helix model of amyloid fibrils proposed recently by Blake and Serpell [Structure 4 (1996) 9899 98]. ß

FT‐Raman spectroscopy as diagnostic tool of Congo red binding to amyloids

“…These data, combined with the fact that silkmoth chorion consists of fibrils similar in appearance to the amyloid fibrils formed from peptide analogues of parts of chorion proteins and structural data of silkmoth chorion presented elsewhere, 7 probably suggest that silkmoth chorion is a natural, protective amyloid that is important for the survival and development of the oocyte and the developing embryo. 7,8 This role is in contrast to that of amyloids associated with serious diseases including Alzheimer's disease, transmissible spongiform encephalopathies, type II diabetes mellitus, and a number of systemic polyneuropathies. 9 -12 Recently, IR, FT-Raman and UV spectroscopy were used to study the binding of Congo red to deposits of Alzheimer's amyloid in cerebral tissue and other typical ␤-amyloid proteins.…”

“…6 We have recently shown that peptide analogues, both of the entire central domain of the A family of silkmoth chorion proteins (cA peptide) and a part of the central domain of the B family of silkmoth chorion proteins (B peptide), form amyloid-like fibrils by self-assembly mechanisms under a great variety of conditions in vitro. 7,8 The fibrils, ϳ100 Å in diameter (Fig. 1), bind Congo red and show the red-green birefringence characteristic for amyloids, when seen under crossed polars (data not shown).…”

“…1), bind Congo red and show the red-green birefringence characteristic for amyloids, when seen under crossed polars (data not shown). Suspensions of these fibrils form oriented fibers, which give characteristic "cross-␤"-X-ray diffraction patterns, 7 a characteristic feature of amyloids as well (see Iconomidou et al 7,8 and references therein). These data, combined with the fact that silkmoth chorion consists of fibrils similar in appearance to the amyloid fibrils formed from peptide analogues of parts of chorion proteins and structural data of silkmoth chorion presented elsewhere, 7 probably suggest that silkmoth chorion is a natural, protective amyloid that is important for the survival and development of the oocyte and the developing embryo.…”

“…Suspensions of these fibrils form oriented fibers, which give characteristic "cross-␤"-X-ray diffraction patterns, 7 a characteristic feature of amyloids as well (see Iconomidou et al 7,8 and references therein). These data, combined with the fact that silkmoth chorion consists of fibrils similar in appearance to the amyloid fibrils formed from peptide analogues of parts of chorion proteins and structural data of silkmoth chorion presented elsewhere, 7 probably suggest that silkmoth chorion is a natural, protective amyloid that is important for the survival and development of the oocyte and the developing embryo. 7,8 This role is in contrast to that of amyloids associated with serious diseases including Alzheimer's disease, transmissible spongiform encephalopathies, type II diabetes mellitus, and a number of systemic polyneuropathies.…”

“…13 Several Raman features attributed to Congo red were found to shift upon amyloid binding, and Raman spectroscopy has therefore been considered a powerful diagnostic tool for ␤-amyloids. In this work we present the FT-Raman spectra of silkmoth chorion, a solid and robust structure consisting of proteins adopting an antiparallel ␤-sheet type of structure, a naturally designed protective amyloid, 6,7 as well as cA peptide amyloid-like fibrils, both unstained and stained with Congo red. Contrary to earlier reports, we provide evidence that the FT-Raman spectra of the stained samples do not provide unequivocal evidence for an amyloid-specific binding of Congo red.…”