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The spider major ampullate (MA) silk exhibits high tensile strength and extensibility and is typically a blend of MaSp1 and MaSp2 proteins with the latter comprising glycine–proline–glycine–glycine-X repeating motifs that promote extensibility and supercontraction. The MA silk from Darwin's bark spider ( Caerostris darwini ) is estimated to be two to three times tougher than the MA silk from other spider species. Previous research suggests that a unique MaSp4 protein incorporates proline into a novel glycine–proline–glycine–proline motif and may explain C. darwini MA silk's extraordinary toughness. However, no direct correlation has been made between the silk's molecular structure and its mechanical properties for C. darwini . Here, we correlate the relative protein secondary structure composition of MA silk from C. darwini and four other spider species with mechanical properties before and after supercontraction to understand the effect of the additional MaSp4 protein. Our results demonstrate that C. darwini MA silk possesses a unique protein composition with a lower ratio of helices (31%) and β-sheets (20%) than other species. Before supercontraction, toughness, modulus and tensile strength correlate with percentages of β-sheets, unordered or random coiled regions and β-turns. However, after supercontraction, only modulus and strain at break correlate with percentages of β-sheets and β-turns. Our study highlights that additional information including crystal size and crystal and chain orientation is necessary to build a complete structure–property correlation model.

Melanin, a widespread pigment found in many taxa, is widely recognized for its high refractive index, ultraviolet (UV) protection, radical quenching ability, metal binding, and many other unique properties. The aforementioned characteristic traits make melanin a potential candidate for biomedical, separation, structural coloration, and space applications. However, the commercially available natural (sepia) and synthetic melanin are very expensive, limiting their use in various applications. Additionally, eumelanin has been the primary focus in most of these studies. In the present study, we demonstrate that melanin can be extracted from the pathogenic black knot fungus Apiosporina morbosa with a yield of ∼10% using the acid–base extraction method. The extracted melanin shows irregular morphology. Chemical characterization using X-ray photoelectron spectroscopy, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy reveals that the melanin derived from black knots is the less explored nitrogen-free allomelanin. Additionally, the extracted melanin shows broadband UV absorption typical of other types of melanin. Because of the wide availability and low cost of black knots and the invasive nature of the fungus, black knots can serve as an alternative green source for obtaining allomelanin at a low cost, which could stimulate its use as an UV light absorber and antioxidant in cosmetics and packaging industries.

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