Proteins of the Crustacean Exoskeleton

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We describe here some of the components of the exoskeleton of the decapod crustacean with emphasis on the constituent proteins, including both structural and enzymatic. All four layers, but particularly the inner three, of the exoskeletons of four brachyurans contain high concentrations of proteins ≤ 31 kDa; the innermost membranous layer is especially rich in such proteins. A number of crab exoskeletal proteins resemble insect cuticle proteins in size (Mr) and isoelectric point (pI). A further similarity is the cross reactivity of crab exoskeletal proteins with four different antibodies against cuticular proteins of two species of insects. One of the small Mr exoskeletal proteins in the Bermuda land crab Gecarcinus lateralis has a similar distribution as a protein of similar size in the cuticle of the tobacco horn worm Manduca sexta. The partial dissolution of an old exoskeleton and formation of the two outer layers of a new exoskeleton are major events in readying a crustacean for the increase in size that occurs at each molt. Expressing both parallel and sequential activation of a number of genes, a single layer of epidermal cells that bounds a crustacean such as G. lateralis synthesizes specific proteins at different stages of the intermolt cycle as the outermost epicuticle and exocuticle are formed during proecdysis and as the endocuticle and membranous layer are formed during metecdysis. Finally, two sets of proteinases isolated from integumentary tissues of land crabs degrade the same exoskeletal proteins in vitro as are degraded in vivo during proecdysis.