Structural Relationships Between Growth Factor Precursors and Cell Surface Receptors

Analysis of the DNA-derived amino acid sequences of several growth factor precursors has revealed the presence of hydrophobic sequences possessing all the characteristics of membrane-spanning domains found in most cell surface receptors. This class of proteins includes the precursors for epidermal growth factor (EGF), transforming growth factor α (TGF-α),and vaccinia virus p19 (pl9vacc). The presence of potential transmembrane domains in these growth factor precursors offers new insight into the evolution of growth factors and their cell surface receptors. The subsequent finding that the EGF precursor shares extensive homology with the low density lipoprotein (LDL) receptor and may not be processed in certain tissues has led to the notion that the EGF precursor may play a dual role as a precursor for a secreted growth factor and, in its unprocessed form, as a cell surface receptor of unknown biological function. Additional distinctive structural features shared by growth factor precursors and growth factor receptors point to a common evolutionary origin for these classes of proteins.