The rubbery sections of preCol-P resemble bovine elastin, which is "very similar" to human elastin, Coyne reports. "Elastins typically are found in the skin and arteries of vertebrate species only," she notes. "The presence of these types of sequences in proteins from an invertebrate species is unusual."
The elastin-like regions of preCol-P also contained high levels of glycine and alanine--the amino acids most prevalent in two forms of protein in spider silk, Waite says. Although the structural similarity between preCol-P and spider silk still must be verified, Waite says the possibility should interest biochemists. "Spider silk is so thin, it has been difficult for anyone but crystallographers to deal with it," he says. "Byssal threads could turn out to be an interesting substitute, or model for studying some aspects of spider silk."
Curiously, the collagenous regions of preCol-P contain a missing glycine. "When a deletion like this is found in other structural collagens," Waite says, "it's certainly lethal to the animal. So, it's quite fascinating to find a missing glycine in a perfectly functional collagen subjected to great stress and strain in marine environments." It's possible, Waite speculates, that the missing glycine creates a 35-degree "kink" or bend in the collagen. But, he adds, "how that might contribute to the stretchiness of the protein is anybody's guess."
Two histidine-rich domains, located at each end of preCol-P, may play a role in forming protein-zinc complexes, Qin says. Whenever histidine-rich domains occur in proteins, they usually bind with metal. In blood, for instance, histidine-loaded glycoprotein binds with zinc. In byssal threads, she says, these domains may react with metals to produce strong "bridges,"
Contact: Ginger Pinholster
University of Delaware