環形動物アオゴカイ Perinereis aibuhitensis 巨大ヘモグロビンのグロビン鎖に含まれる稀有な SS 結合 Novel S-S loops in the globin chains from the giant hemoglobin of the polychaete Perinereis aibuhitensis
The extracellular hemoglobin (Hb) from the polychaete Perinereis aibuhitensis consistsof four types of 144 globins and two types of 36 linker chains，having a molecular mass of about 3,500kDa. There are two types of globin subunits: monomer chain a and disulfide-bondedt rimer AbB. Theamino acid sequences of the four globin chains (a，A ，b ，B ) were already reported，previously(Yamanaka，M. et al. Natural Science Research of Tokushima University, 19, 63-92, 2005). The site of disulfide bonds in the globin subunits have been investigated. Each globin chain contains an intrachaindisulfide bond between N-terminal and C-terminal Cys residues. In addition，the interchain disulfidebonds were found between chains A and b，and b and B. Therefore，it is elucidated that the chain b issituated at the center of disulfide-bonded trimer，such as A-b-B.The sites of disulfide-bonds determinedall could be suitably fitted to the tree dimensional structure of each subunit in a model withoutstretching or twisting. It was also confirmed that there is no free Cys residue in Peinereis globins. Thepositions of Cys residues of Perinereis globin sequences were compared wIth those of other 27 chainsderived from the homologous Hbs. Among 31 sequences，Cys residues were distributed in six sites.The sites 1 and 2 are located at the N-terminal region of amino acid sequences，the sItes 3 and 4 at thecentral region，and the sites 5 and 6 at C-terminal region. Furthermore，the Cys distribution wascategorized into eight patterns. Perinereis Hb has four patterns I，IV，VII，VIII，be ing lack of the centralsites 3 and 4. It should be noted that the pattern II includes the unique globins from Hbs of Lamellibrachia，Riftiaand Oligobrachia that carry H2S to the symbiotic bacteria，suggesting that these globin chains might carry H2S invivo. The phylogenetic tree of 31 globin chains derived from the giant Hbs is divided into two families A and B，as already poited out by us Previously. The family A indudes pattern I-V，whereas the family B includes V-VIII.
徳島大学総合科学部自然科学研究 22, 105-125, 2008-12