CHARACTERIZATION OF EXOSKELETAL PROTEINS FROM THE AMERICAN LOBSTER, HOMARUS-AMERICANUS

Proteins from the calcified exoskeleton of the lobster, Homarus americ anus, were extracted and separated by two-dimensional gel electrophore sis. Electroblotting the proteins onto polyvinylidene difluoride (PVDF ) membranes followed by sequence determination gave 16 N-terminal amin o acid sequences and revealed that further eight proteins were N-termi nally blocked. The relative molecular mass, M-r, was obtained for most of the electrophoretically separated proteins by means of matrix-assi sted laser desorption mass spectrometry (MALDIMS) after electroelution from Coomassie-stained two-dimensional polyacrylamide gels. Eleven pr oteins were purified from extracts of the exoskeleton by low pressure ion exchange chromatography and reversed-phase high performance chroma tography, and their sequences were determined by combined use of Edman degradation and mass spectrometry. Good agreement was obtained betwee n the M-r-values measured by mass spectrometry and those calculated fr om the sequences. Five of the sequenced proteins contain two copies of a previously observed 18-residue sequence motif, while a couple of th e remaining sequences show similarity to sequences of exoskeletal prot eins from shrimps and spiders. Only limited similarity to insect cutic ular proteins was observed. (C) 1998 Elsevier Science Inc.