PRIMARY STRUCTURE OF A CONSTITUENT POLYPEPTIDE-CHAIN OF THE CHLOROCRUORIN FROM SABELLASTARTE INDICA

A 16 kDa polypeptide chain (chain E) was isolated from the giant extracellular chlorocruorin from the polychaete Sabellastarte indica by reverse-phase chromatography, and the N-terminal 19 amino-acid residues was determined by an automated protein sequencer. The cDNA of Sabellastarte chain E was amplified by polymerase chain reaction (PCR), and the complete nucleotide sequence of 1205 bp was determined. The open reading frame is 498 nucleotides in length and encodes a protein with 165 amino-acid residues. Comparison of the cDNA-derived amino-acid sequence with the protein sequence shows that Sabellastarte chain E has a signal peptide of 16 residues at the N-terminus, the mature protein consisting of 149 amino-acid residues with a calculated molecular mass of 16636 Da. The amino-acid sequence of Sabellastarte chain E shows 42-49% sequence identity with the corresponding chains of the giant hemoglobins from Tylorrhymchus (polychaete, Annelida), Lumbricus (oligochaete, Annelida), Lamellibrachia (Vestimentifera) and Oligobrachia (Pogonophora). Thus, we conclude that chlorocruorin with chlorocruorohaem falls into the 'hemoglobin/myoglobin family'. This is the first complete sequence of a globin polypeptide chain of a chlorocruorin.