Molecular cloning and characterisation of a proteinase inhibitor, alpha 2-macroglobulin (α2-M) from the haemocytes of tiger shrimp Penaeus monodon

The alpha 2-macroglobulin cDNA from tiger shrimp Penaeus monodon consists of 4876 bp and encodes a protein of 1498 amino acids.

• The open reading frame includes a 52 bp 5'-untranslated region and a 327 bp 3'-untranslated region containing a poly A signal.
• The mature protein has an estimated molecular mass of 167.7 kDa and a predicted isoelectric point of 5.30.
• Functional domains identified in the protein include a thioester region, a bait region, and a receptor-binding domain.
• The deduced amino acid sequence exhibits 85%, 52%, and 49% similarity to alpha2-M sequences from kuruma shrimp, American horseshoe crab, and mud crab, respectively.
• Alpha2-M is predominantly expressed in haemocytes, showing a significant increase in mRNA transcripts after peptidoglycan injection at 12, 24, and 48 hours, returning to baseline by 72 hours.

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