ScienceDaily (Nov. 25, 2007) — Web-making spiders employ a host of silk glands to synthesize a variety of silk filaments with different mechanical properties. Although it is widely believed that the aciniform glands are one such silk factory, there has been no hard evidence linking aciniform-derived proteins and silk --until now.

Craig Vierra and colleagues found that the aciniform gland in the Black Widow manufactures and extrudes a previously unidentified protein that is a component of multiple types of silk.

Vierra and colleagues used mass spectroscopy to analyze the protein content of two types of silk: the variety used for egg cases and the one used to wrap up prey. In both types they uncovered a thin protein fiber with a similar structure to another known silk protein called AcSp1. When they examined the expression of this new protein, termed AcSp1-like protein, in different silk glands, they found that mRNA levels were present at 1000-fold higher concentration in the aciniform gland compared to other glands.

The researchers note this finding is intriguing since it shows that aciniform silk fibers are not made for one specific task but rather get integrated into multiple silk types. They plan to further characterize the mechanics of aciniform silk, but they propose that this thin fiber acts like twine to hold thicker silk fibers together.

Journal article: "Aciniform spidroin: A constituent of egg case sacs and wrapping silk fibers from the black widow spider, Latrodectus Hesperus" by Keshav Vasanthavada, Xiaoyi Hu, Arnold M. Falick, Coby LaMattina, Anne M.F. Moore, Patrick R. Jones, Russell Yee, Ryan Reza, Tiffany Tuton, and Craig A. Vierra

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Prey wrap silk contains small diameter fibers that contain AcSp1-like protein molecules. (Credit: Craig Vierra)

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