Characterization of lamprin, an unusual matrix protein from lamprey cartilage. Implications for evolution, structure, and assembly of elastin and other fibrillar proteins.

Abstract

Lamprin, an insoluble non-collagen, non-elastin protein, is the major connective tissue component of the fibrillar extracellular matrix of lamprey annular cartilage. Here we demonstrate that the soluble monomer of lamprin is a family of highly hydrophobic, self-aggregating proteins with molecular masses of 12 and 10 kDa. Two mRNAs for soluble lamprin were identified (0.9 and 2 kilobases), differing principally in the length of their 3'-untranslated tails. Variants of soluble lamprin appear to arise both as the products of multiple genes and by alternate splicing. Although not generally homologous to any other protein, soluble lamprins contain a tandemly repeated peptide sequence (GGLGY) which is present in both silkmoth chorion proteins and spider dragline silk. Strong homologies to this repeat sequence are also present in several mammalian and avian elastins. Monoclonal antibodies to VGVAPG, a repeated sequence in human elastin, also cross-react with lamprin. We suggest that these proteins share a structural motif which promotes self-aggregation and fibril formation in proteins through interdigitation of hydrophobic side chains in beta-sheet/beta-turn structures, a motif that has been preserved in recognizable form over several hundred million years of evolution.