Model for haptoglobin heavy chain based upon structural homology.

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Abstract
A model was constructed for haptoglobin heavy chain by using the known sequence homology to the mammalian serine proteases. The 3-dimensional structures for 3 serine proteases, chymotrypsin, trypsin and elastase, were compared and the structural features that are conserved in all 3 were extracted. The haptoglobin heavy chain sequence was aligned to the sequences of the 3 serine proteases by maximizing sequence homology in the regions of conserved structure. The resulting alignment shows that haptoglobin heavy chain must be very closely homologous to these proteases in structure and in sequence. Coordinates were derived for the heavy chain by using the homologous structures. The problems associated with these coordinates are outlined and methods for solving them are indicated. The features of the haptoglobin heavy chain structure are described. Implications of the structure for the very strong interaction between this subunit and Hb are discussed.