Curious Forms of Collagen
To find out what makes byssal threads so special, Qin and Waite first isolated two key collagens: Col-P and Col-D. They used pepsin, an enzyme secreted by stomach cells of vertebrates, to pinpoint the collagens. Unlike most proteins, Waite says, Col-P and Col-D don't break apart in response to pepsin. Since pepsin works best in an acidic environment, researchers simply placed byssal threads and pepsin in a weak solution of acetic acid. "Col-P and Col-D were the only proteins detectable after pepsinization," Waite explains. "Within byssal threads, these two collagens are distributed in a complementary gradient, with Col-P predominant in the elastic, proximal region, near the foot of the mussel, and more Col-D at the far, or distal end."
The UD team also examined the protein precursors for Col-P and Col-D, found in the mussel foot, where byssal threads are produced. Specific antibodies--proteins designed to detect and fight off foreign molecules by binding with them--helped Coyne target preCol-P. First, messenger RNA (ribonucleic acid) containing the genetic code for the protein was extracted from mussel foot tissue. Next, RNA was converted to the more stable DNA (deoxyribonucleic acid) form and cloned into bacteria, which expressed the protein encoded by the mussel's RNA. Designer antibodies, produced by a laboratory animal injected with Col-P, quickly latched onto the protein precursor expressed by bacterial clones.
Three Major Domains
The preCol-P in byssal threads contains three major domains, Coyne says. The middle section
Contact: Ginger Pinholster
University of Delaware