Comparison of Haliotis rubra hemocyanin isoforms 1 and 2

• We cloned full-length cDNAs encoding Haliotis rubra hemocyanin isoforms 1 and 2.
• Haliotis rubra hemocyanin is closely related to Haliotis tuberculata hemocyanin.
• Protein sequence comparison suggests functional differences.

We have obtained for the first time the complete cDNA sequences encoding the two known hemocyanin isoforms from the mollusc Haliotis rubra. Based on the predicted amino acid sequence each isoform has an almost identical estimated molecular mass of ~ 390 kDa. The isoforms share an amino acid sequence similarity of 66% and consist of eight functional units (FUs a–h) separated by variable linker regions. As observed in other molluscan hemocyanins, FU-h has a C-terminal extension of ~ 100 amino acids. The presence of a conserved di-copper binding domain in each FU, which contributes to hemocyanin's role as an oxygen transporter, was also confirmed. The most closely related sequences to H. rubra were those of the hemocyanin isoforms from Haliotis tuberculata with a homology of > 90%. Like the hemocyanin isoforms from H. tuberculata, the H. rubra versions contain several predicted N-linked glycosylation sites. The predicted N-linked glycosylation pattern of H. rubra hemocyanin isoforms is highly similar but not identical to H. tuberculata hemocyanin isoforms. Such differences may translate to variations in structural organisation of these oligomeric proteins or in other known functions of hemocyanin such as innate immunity or antiviral activity. Knowledge of the complete cDNA sequences of H. rubra hemocyanin isoforms will allow mapping of minimal domain(s) required for these functions.