Cell-surface receptors: puzzles and paradigms

The determination of amino acid sequences representing the cell-surface receptors for transferrin,¹ asialoglycoprotein,² polymeric immunoglobulin (IgA/IgM),³ epidermal growth factor (EGF),⁴ lowdensity lipoprotein (LDL)⁵ and insulin⁶ has produced new paradingms for receptor architecture. This review examines common features of the protiens and describes the intriguing functional and evolutionary puzzles that have arisen from them.