Xanthurenic Acid Is the Main Pigment of Trichonephila clavata Gold Dragline Silk

Abstract

Spider silk is a natural fiber with remarkable strength, toughness, and elasticity that is attracting attention as a biomaterial of the future. Golden orb-weaving spiders (Trichonephila clavata) construct large, strong webs using golden threads. To characterize the pigment of golden T. clavata dragline silk, we used liquid chromatography and mass spectrometric analysis. We found that the major pigment in the golden dragline silk of T. clavata was xanthurenic acid. To investigate the possible function of the pigment, we tested the effect of xanthurenic acid on bacterial growth using gram-negative Escherichia coli and gram-positive Bacillus subtilis. We found that xanthurenic acid had a slight antibacterial effect. Furthermore, to investigate the UV tolerance of the T. clavata threads bleached of their golden color, we conducted tensile deformation tests and scanning electron microscope observations. However, in these experiments, no significant effect was observed. We therefore speculate that golden orb-weaving spiders use the pigment for other purposes, such as to attract their prey in the sunlight.

Molecular atlas reveals the tri-sectional spinning mechanism of spider dragline silk

“…Moreover, the XA was further confirmed by LC-MS analysis of the golden extract (Fig. 2e), consistent with a recent report 21 .…”

“…For example, of the major ampullate spidroins (MaSps), recombinant repetitive motifs were constructed to achieve specific physical properties, including strength, extensibility, and stickiness, for silk [17][18][19] . Spider silk-constituting elements (SpiCEs), nonspidroin proteins, are utilized to increase tensile strength in the case of composite silk films [20][21][22] . In addition, the microfluidics device designed to realize the closest equivalent to natural ionic and pH conditions allows the fibers to be directly pulled out from the outlet and then reeled in air, as in native spinning [23][24][25] .…”

“…Thus far, comprehensive genomic analyses of orb-web spiders have parsed the molecular traits of MaSps as well as other nonspidroin proteins composing dragline silk 17,21,[28][29][30][31] . Nevertheless, genetically mediated Ma gland mechanisms underlying dragline silk production remain poorly understood.…”

Xanthurenic Acid in the Shell Purple Patterns of Crassostrea gigas: First Evidence of an Ommochrome Metabolite in a Mollusk Shell

“…For examples, the red, red-brown and yellow pigments of wings of Junonia coenia (common buckeye) were attributed to dihydroxanthommatin, ommatin D and xanthommatin (ommochromes of the ommatin type) but none were detected by MS/MS liquid chromatography, in contrast to XA [ 10 , 32 ]. Indeed, in invertebrates, XA is described as a key metabolite of the biosynthesis of ommochromes [ 12 , 13 , 18 , 19 ], exclusively related to this biological route [ 12 ]. To date, two main biosynthetic pathways of ommochrome pigments have been proposed, both involving XA.…”

“…These represent only a small proportion of the overall acid-soluble pigments among which, the occurrence of ommochromes would corroborate the recent identification of genes associated with their biosynthetic pathways [ 9 ]. However, the precise chemical structure of ommochromes is generally unknown at present, their occurrence in a natural sample is usually postulated by the identification of specific biosynthetic metabolites such as 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid (3-HA) and XA [ 10 , 11 , 12 , 13 ].…”