Structural Properties of Phycoerythrin from Dulse Palmaria palmata

We found that the red alga dulse (Palmaria palmata) contains a lot of proteins, which is mainly composed of phycoerythrin (PE) and the protein hydrolysates showed high angiotensin I converting enzyme (ACE) inhibitory activities. Therefore, we investigated the structure of dulse PE to discuss its structure-function relationship. We prepared the chloroplast DNA and analyzed the nucleotide sequences encoding PE by cDNA cloning method. It was clarified that dulse PE has α- and β-subunits and they are composed by 164 amino acids (MW: 17,638) and 177 amino acids (MW: 18,407), respectively. The dulse PE contained conserved cysteine residues for chromophore attachment site. On the alignment of amino acid sequences of dulse PE with those of other red algal PE, the sequence identities were very high (81–92%). In addition, we purified and crystallized the dulse PE, and its crystal structure was determined at 2.09 Å resolution by molecular replacement method. The revealed 3D structure of dulse PE which forms an (αβ)₆ hexamer was similar to other red algal PEs. Conversely, it was clarified that the dulse PE proteins are rich in hydrophobic amino acid residues (51.0%), especially aromatic amino acid and proline residues. The data imply that the high ACE inhibitory activity of dulse protein hydrolysates would be caused by the specific amino acid composition and sequence of dulse PE. Practical Applications: Dulse is an abundant and underused resource, which contains a lot of phycobiliproteins. Then, the dulse protein hydrolysates strongly inhibited the activity of ACE. Therefore, it has the potential to be an ingredient of functional food.