Human and murine phosphorycholine-binding immunoglobulins: conserved subgroup and first hypervariable region of heavy chains.

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Abstract
The NH2-terminal 36 residues of the H chain and the NH2-terminal 40 residues of the L chain from a human Waldenstroem''s IgM [immunoglobulin M] with binding activity for phosphorylcholine (phosphocholine) are compared with the published sequences of 5 mouse IgA myeloma proteins with the same activity. An extensive structural similarity, i.e., 3 amino acid interchanges within framework residues, and 1 in the hypervariable region, is noted between the H chains of both species. The L chains show a considerable diversity and, in contrast to the H chain, no correlation between the primary structure of the 1st hypervariable region and the binding specificity is apparent. The finding of a very similar H chain variable region in 2 different species that are separated by about 75 million yr in evolution favors the concept of stable transmission of variable region genes throughout evolution.