title: The muscle-derived lens of a squid bioluminescent organ is biochemically convergent with the ocular lens. Evidence for recruitment of aldehyde dehydrogenase as a predominant structural protein.
abstract: Many of the structural proteins of ocular lenses, commonly referred to as crystallins, are identical to specific enzymes or the result of a recent gene duplication (Piatigorsky, J., and Wistow, G. (1991) Science 252, 1078-1079). One such enzyme, aldehyde dehydrogenase (ALDH), has been recruited as a lens crystallin in certain mammals (Wistow, G., and Kim, H. (1991) J. Mol. Evol. 32, 262-269) and cephalopods (Tomarev, S., Zinovieva, R., and Piatigorsky, J. (1991) J. Biol. Chem. 266, 24226-24231). We report here that a transparent tissue, derived from muscle but functioning as a lens in the light-emitting organ of a squid, Euprymna scolopes, shows striking biochemical convergence with the epidermally derived ocular lenses of some mammals and cephalopods. In the light organ lens of E. scolopes, an ALDH-like protein is the predominant molecular component. The typical muscle-specific proteins are replaced as the dominant species by a protein composed of 54-kDa subunits. This protein, which we designate as L-crystallin, constitutes approximately 70% of the total soluble protein of the light organ lens. The amino acid sequences of three peptides of L-crystallin (approximately 9% of the total protein) showed 54.5% sequence identity with human cytosolic ALDH. Using polyclonal antiserum made against L-crystallin, we found that it is present in low abundance in other tissues of the squid, including muscle and the ocular lens. This polyclonal antiserum also cross-reacted with the ALDH-like crystallins found in the ocular lenses of certain mammals and cephalopods. L-Crystallin showed no ALDH activity, which is similar to several other enzyme/crystallins, including ALDH/eta-crystallin (Wistow, G., and Kim, H. (1991) J. Mol. Evol. 32, 262-269). The characteristics of this muscle-derived lens are evidence that a common biochemical basis underlies transparency and that certain proteins may possess properties that promote their selection as lens structural proteins.
authors.affiliation: Department of Biological Sciences, University of Southern California, Los Angeles 90089-0371.
authors.forename: M K
authors.initials: MK
authors.lastname: Montgomery
authors.forename: M J
authors.initials: MJ
authors.lastname: McFall-Ngai
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics* / Q000302:isolation & purification; D000595:Amino Acid Sequence; D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000235:genetics* / Q000302:isolation & purification; D049832:Decapodiformes; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007908:Lens, Crystalline / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D008163:Luminescent Measurements; D008969:Molecular Sequence Data; D009132:Muscles / Q000502:physiology*; D017386:Sequence Homology, Amino Acid
chemical_list: D003459:Crystallins; D000444:Aldehyde Dehydrogenase