LAUSR

ABSTRACT Five different serine protease homologs (SPH) transcripts presumably or possibly resulting from alternative splicing were cloned from the hemocytes of crayfish (Procambarus clarkii) in this paper. Although different deletions of cDNA of SPH-2 and SPH-4 were found in the 5ʹ untranslated regions, they shared the same open reading frame and encoded a 424 amino acids protein with a calculated molecular weight of 45.84 kDa compared with SPH-5. The predicted cutting site of the signal peptide was located between Ala22 and Glu23; a clip domain and a trypsin-like serine protease domain were located in the N-terminal and the C-terminal, respectively. Large deletions were found in the SPH-1 and SPH-3. Both of them lacked the clip domain. The 22 amino acids signal peptide existed in the SPH-1 coding protein, and a low complexity region (LCR) was formed in the N-terminal of it. The deduced protein of SPH-1 contained 358 amino acids with a molecular weight of 38.80 kDa. There was only one trypsin-like serine protease domain found in the C-terminal of the SPH-3 coding protein. The deduced protein of SPH-3 contained 250 amino acids with a molecular weight of 26.90 kDa. The amino acid Ser (S) of the catalytic triad in trypsin-like serine protease domain of the proteins analyzed in this paper was replaced by Gly (G), suggesting that the SPH-1, SPH-2, SPH-3, SPH-4, and SPH-5 were serine protease homologs.