PROTEINS OF CRUSTACEAN EXOSKELETON .4. PARTIAL AMINO-ACID-SEQUENCES OF EXOSKELETAL PROTEINS FROM THE BERMUDA LAND CRAB, GECARCINUS-LATERALIS, AND COMPARISONS TO CERTAIN INSECT PROTEINS

As in all decapod Crustacea, the exoskeleton of the land crab Gecarcin us lateralis consists of four layers. Prior electrophoretic analysis o f proteins extracted from these layers revealed an abundance of small M(r) proteins with acidic pIs as are found in insect cuticle (O'Brien et al. [1991 Biol. Bull., 181:427-441). Further, immunological cross-r eactivity between crab exoskeletal proteins and insect cuticular prote ins has been demonstrated (Kumari and Skinner [1993] J. Exp. Zool., 26 5:195-210). Partial amino acid sequences of a number of proteins from the four exoskeletal layers are described here. Proteins were electrop horesed on two-dimensional (2D) gels, transferred to polyvinylidene di fluoride (PVDF) membranes, and stained; individual spots were recovere d and their N-termini were sequenced. In addition, a 14-kDa protein (p i = 5.4) from membranous layer (ML14) was eluted from 2D gels and dige sted with endoproteinase Lys-C; N-termini of its constituent peptides were sequenced. The two epicuticular proteins differed from each other . Three proteins with identical electrophoretic mobility isolated from exocuticle, endocuticle, and membranous layer appeared to have identi cal N termini, while another electrophoretically identical set from th e three layers appeared identical with each other but differed in thre e positions from the first set. Two proteins from the membranous layer both had a mass of 25 kDa but different isoelectric points. Their seq uences were indistinguishable from each other but clearly distinct fro m another membranous layer protein. Another distinct sequence was foun d in a 14-kDa protein from endocuticle, while a less acidic pair of 14 -kDa proteins from endocuticle and membranous layer were quite similar to one another. The three internal peptide fragments from ML14 were d istinct, but one had regions similar to the ML14 N terminus. One crab exoskeletal protein sequence was similar to some structural proteins o f vertebrates, whereas others had motifs found in insect cuticular pro teins. The sequence similarities identified did not account for the an tibody cross-reactivity. (C) 1995 Wiley-Liss, Inc.