Researchers from USA and Slovenia have made a major advance with the largest-ever study of spider silk genes! As they report today in an advance online paper in Nature Genetics, the scientists sequenced the full genome of the golden orb-weaver spider (Nephila clavipes), a prolific silk-spinner that turns out to produce 28 varieties of silk proteins. In addition to cataloguing new spider silk genes, the researchers discovered novel patterns within the genes that may help to explain the unique properties of different types of silk.
“There were so many surprises that emerged from our study: new silk genes, new DNA sequences that presumably confer strength, toughness, stretchiness and other properties to silk proteins; and even a silk protein made in venom glands rather than silk glands,” said senior author Benjamin F. Voight, PhD, an associate professor in the departments of Genetics and Systems Pharmacology and Translational Therapeutics. “All this new information should greatly advance our efforts to capture the extraordinary properties of these silks in man-made materials.”
Even though spider silks have been studied for more than 50 years, earlier foundational work had identified only a comparative handful of spider silk genes. Even recent work from species with smaller silk repertoires than the golden orb-weaver’s were incomplete. To find all of the silk genes hidden across the golden orb-weaver’s genome—the veritable “lab rat” of spider silk science—required the construction of the entire genome, a daunting task in itself.
Spidroins have been classified into seven categories according to their protein sequences and functions. An extensive computational analysis of the orb-weaver’s spidroin genes revealed nearly 400 short sequences—many never before described—that appear repeatedly in these genes with small variations and in different combinations. These repetitive spidroin “motifs” are of great interest to biologists and engineers because they are likely to confer the key properties of a given spider silk, such as high tensile strength, flexibility, or stickiness.
Voight’s team also examined gene transcripts from different orb-weaver silk glands and in each case found transcripts belonging to more than one spidroin class, suggesting that these glands are not strictly specialized for producing one type of silk.
“We found significantly more complexity in silk production than we expected,”
The biggest surprise was the discovery that one of the orb-weaver’s spidroins—FLAG-b, a novel discovery by the group—appears to be produced primarily in the orb-weaver’s venom gland rather than in any silk gland, hinting at intriguing new functions for silk connected to prey capture, immobilization, or preservation.
In their analyses of the genome data, Voight and colleagues also identified 649 likely genes that are not spidroin genes but are highly expressed in silk glands, and thus probably have roles in converting the liquid silk from spider cells into solid, spinnable threads—a tricky process that biotech engineers are just beginning to achieve outside of spiders.
Voight and his team are now following up with a genome-sequencing study of Darwin’s bark spider, which makes the strongest known silks, and has been known to span rivers with them.