Structural hierarchy in erythrocruorin, the giant respiratory assemblage of annelids
Graduate School of Biomedical Sciences; Department of Biochemistry and Molecular Pharmacology
Life Sciences | Medicine and Health Sciences
Many annelids, including the earthworm Lumbricus terrestris, have giant cooperative respiratory proteins (molecular masses greater than 3.5 million Da) freely dissolved in the blood, rather than packaged in cells. These complexes, termed either erythrocruorins or hemoglobins, are assembled from many copies of both hemoglobin subunits and nonhemoglobin or "linker" subunits. In this paper, we present the crystal structure of Lumbricus erythrocruorin at 5.5-A resolution, which reveals a remarkable hierarchical organization of 144 oxygen-binding hemoglobin subunits and 36 nonhemoglobin linker subunits. The hemoglobin chains arrange in novel dodecameric substructures. Twelve trimeric linker complexes project triple-stranded helical coiled-coil "spokes" toward the center of the complex; interdigitation of these spokes appears crucial for stabilization. The resulting complex of linker chains forms a scaffold on which twelve hemoglobin dodecamers assemble. This structure specifies the unique, self-limited assemblage of a highly cooperative single molecule.
Proc Natl Acad Sci U S A. 2000 Jun 20;97(13):7107-11.
Proceedings of the National Academy of Sciences of the United States of America
Royer, William E.; Strand, Kristen; van Heel, Marin; and Hendrickson, Wayne A., "Structural hierarchy in erythrocruorin, the giant respiratory assemblage of annelids" (2000). GSBS Student Publications. 1031.