A MOLECULAR-MODEL FOR THE D-CHAIN OF THE GIANT HEMOGLOBIN FROM LUMBRICUS-TERRESTRIS AND ITS IMPLICATIONS FOR SUBUNIT ASSEMBLY

A structural model for the monomeric d chain of the giant haemoglobin from Lumbricus terrestris is described. Based on the crystal structure s of other globins, the model provides evidence for the existence of a novel tryptophan-haem interaction. The observation that all three try ptophans are buried within the hydrophobic core is consistent with flu orescence data on the isolated monomer and the intact molecule. The mo del has also been used to predict the probable arrangement of the abcd tetramer as being similar to that observed in the clam Hb II structur e. Such predictions allow the identification of four residues of parti cular importance in stabilising one of the subunit-subunit interfaces: Arg48, Arg97, His89 and Gln93. The latter two may be of special impor tance in the mediation of cooperative effects within the tetramer and indeed the intact molecule. (C) 1998 Elsevier Science B.V.