Identification of the subunit loci in the extracellular multisubunit hemoglobin from annelid Perinereis aibuhitensis.
Giant hemoglobin (Hb) from Perinereis aibuhitensis is made of several types of protein components including single-chain globin (a), disulfide-bridged globin trimer (A-b-B), disulfide-bridged dimers of nonglobin chain (or linkers; L1-L1, L2-L2, and L1-L2), and oligomers of L1-L2 [(L1-L2)n]. The intact form of this giant Hb is a two-tiered hexagonal structure composed of 12 identical units, or so-called submultiples (six submultiples to a tier). To obtain a view of the three-dimensional architectural arrangement of these components in the intact form, we identified the subunit loci by using two mutually complementary chemical modifications and a colloidal gold labeling technique. Using the chemical modifications, we discovered that (i) linkers L1-L2 and L2-L2 were located at the exterior of the Hb, (ii) linker L1-L1 and globin a were buried in the interior, and (iii) linker (L1-L2)n and globin trimer A-b-B were located at both exterior and interior loci. The labeling with an L2-specific colloidal gold revealed the predominant loci of L2 at the outer and inner boundaries between neighboring submultiples in a hexagonal form. By combining these results with those from our previous reports [S. Ebina, K. Matsubara, K. Nagayama, M. Yamaki, and T. Gotoh (1995) Proc. Natl. Acad. Sci. USA 92, 7367-7371; K. Matsubara, M. Yamaki, Nagayama, H. Ishii, K. Imai, T. Gotoh, and S. Ebina (1996), in press], we deduced the following conclusions concerning the Hb architecture. The L1-L1 chains perhaps together with (L1-L2)n chains form a scaffold on which submultiples assemble into a two-tiered hexagonal arrangement, probably by connecting the carbohydrates in globin a. The L1-L2 and L2-L2 chains reinforce the connections of the submultiples by binding carbohydrates, perhaps those carbohydrates in globin A. We proposed to call this type of non-protein-dependent structural level as seen in such a carbohydrate-glued protein aggregate "protein-plus structure."
L'Oréal Tsukuba Center, Japan.
M
M
Yamaki
K
K
Matsubara
A
A
Shibuya
T
T
Gotoh
S
S
Ebina
D000818:Animals; D000845:Annelida; D003432:Cross-Linking Reagents; D004220:Disulfides; D004591:Electrophoresis, Polyacrylamide Gel; D016650:Fluorescein-5-isothiocyanate; D005914:Globins / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure*; D007700:Kinetics; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008961:Models, Structural
D003432:Cross-Linking Reagents; D004220:Disulfides; D006454:Hemoglobins; D046911:Macromolecular Substances; D005914:Globins; D016650:Fluorescein-5-isothiocyanate