MOLECULAR SYMMETRY OF THE DODECAMER SUBUNIT OF LUMBRICUS-TERRESTRIS HEMOGLOBIN

The principal functional subunit of the similar to 3500 kDa extracellu lar Lumbricus terrestris hemoglobin is a 213 kDa dodecamer of four che mically distinct globin chains, consisting of a non-covalent complex o f three trimer submits (disulfide-bonded chains a, b and c) and three monomer subunits (chain d). X-ray diffraction of crystals of the dodec amer grown at neutral pH, were found to be monoclinic, with the unit c ell dimensions: a=112.3 Angstrom, b = 190.0 Angstrom, c = 69.6 Angstro m, beta = 102.0 degrees with h + k + l = 2n + 1 absent, characteristic of space group I121. In addition, these crystals exhibit a pseudo tri gonal P321 symmetry with unit cell dimensions a = 190.5 Angstrom, b = 190.5 Angstrom, c = 69.5 Angstrom, gamma = 120.0 degrees. Assuming tha t the assymetric unit contains an entire dodecamer, a model of the lat ter was constructed that satisfies the symmetry of the trigonal pseudo cell and is consistent with the symmetry of the I121 crystallographic cell. The resulting model has strong implications concerning the hexa gonal bilayer structure of the native hemoglobin. (C) 1996 Academic Pr ess Limited