Molecular cloning and phylogenetic analysis on α2-macroglobulin (α2-M) of white shrimp Litopenaeus vannamei

The full-length sequence of α2-macroglobulin (α2-M) was cloned from the hemocytes of white shrimp Litopenaeus vannamei by reverse transcription polymerase chain reaction (RT-PCR), cloning and sequencing of overlapping PCR, and the rapid amplification of cDNA ends method. The α2-M cDNA consists of 4682 bp with an open reading frame of 4479 bp, a 52-bp 5′-untranslated region, and a 132-bp 3′-untranslated region. The predicted molecular mass of the mature protein (1475 amino acids) is 167.1 kDa, with an estimated pI of 5.70. The L. vannamei α2-M sequence contains putative functional domains including a bait region, a GCGEQNM (985-991) thiol ester domain, and a receptor-binding domain. Sequence comparison and phylogenetic analyses show that α2-M deduced amino acid sequence of L. vannamei has a high level of similarity to that of tiger shrimp Penaeus monodon and kuruma shrimp Marsupenaeus japonicus. The α2-M transcript was mainly expressed in hemocytes, and was significantly higher in premoult stage than in intermoult and postmoult stages.