J3-Crystallin of the Jellyfish Lens: Similarity to Saposins

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 98; no. 22; pp. 12362 - 12367
• Main Authors: Piatigorsky, Joram, Norman, Barbara, Dishaw, Larry J., Kos, Lidia, Horwitz, Joseph, Steinbach, Peter J., Kozmik, Zbynek
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 23-10-2001; National Acad Sciences; The National Academy of Sciences
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Biochemistry; Biological Sciences; Cnidaria; Complementary DNA; Crystallins; Crystallins - chemistry; Crystallins - genetics; Crystallins - physiology; DNA, Complementary - isolation & purification; Enzymes; Exons; Eyes & eyesight; Fish; Glycoproteins - chemistry; J3-crystallin; Jellyfishes; Marine; Messenger RNA; Molecular Sequence Data; Ocelli; Proteins; RNA; RNA, Messenger - analysis; Saposins; Scyphozoa - chemistry; Sphingolipid Activator Proteins; Tripedalia cystophora; Vertebrates
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.231310698

J3-crystallin, one of the three major eye-lens proteins of the cubomedusan jellyfish (Tripedalia cystophora), shows similarity to vertebrate saposins, which are multifunctional proteins that bridge lysosomal hydrolases to lipids and activate enzyme activity. Sequence alignment of deduced J3-crystallin indicates two saposin-like motifs arranged in tandem, each containing six cysteines characteristic of this protein family. The J3-crystallin cDNA encodes a putative precursor analogous to vertebrate prosaposins. The J3-crystallin gene has seven exons, with exons 2-4 encoding the protein. Exon 3 encodes a circularly permutated saposin motif, called a swaposin, found in plant aspartic proteases. J3-crystallin RNA was found in the cubomedusan lens, statocyst, in bands radiating from the pigmented region of the ocellus, in the tentacle tip by in situ hybridization, and in the embryo and larva by reverse transcription-PCR. Our data suggest a crystallin role for the multifunctional saposin protein family in the jellyfish lens. This finding extends the gene sharing evolutionary strategy for lens crystallins to the cnidarians and indicates that the putative primordial saposin/swaposin J3-crystallin reflects both the chaperone and enzyme connections of the vertebrate crystallins.