A potential mediator of collagenous block copolymer gradients in mussel byssal threads.
Mussel byssal threads contain unusual block copolymer-like proteins that combine collagen with flanking domains that resemble silk-fibroin (preCol-D) or elastin (preCol-P). These are distributed in complementary gradients along the length of the threads and as precursors in the mussel foot. We discuss a 76-kDa precursor, preCol-NG, from a cDNA library of the foot where it has no gradient but rather is distributed evenly along the distal to proximal axis. A pepsin-resistant fragment of preCol-NG has been confirmed in byssal threads. Like preCol-D and -P, this protein has a central collagenous domain, flanking domains, an acidic patch, and histidine-rich termini. The flanking domains of preCol-NG resemble the glycine-rich proteins of plant cell walls with tandem XGlyn repeats where X denotes alanine, leucine, or asparagine but not proline. Similarity with the (glycine-alanine) repeats and poly(alanine) runs of arthropod silks also exists. Based on available evidence, a model of preCol axial assembly is proposed in which preCol-NG functions as a mediator between preCol-D/-P molecules. This is consistent with the observed progression of mechanical properties in byssal threads.
Marine Biology/Biochemistry Program, University of Delaware, Newark, DE 19716, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001704:Biopolymers; D049872:Bivalvia / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003094:Collagen / Q000737:chemistry* / Q000302:isolation & purification; D017931:DNA Primers; D008969:Molecular Sequence Data; D009132:Muscles / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
D001704:Biopolymers; D017931:DNA Primers; D003094:Collagen