Sequence‐specific

Abstract CD59 is a recently discovered cell‐surface glycoprotein that restricts lysis by homologous complement and has limited sequence similarity to snake venom neurotoxins. This paper describes the first results of a two‐dimensional NMR study of CD59 prepared from human urine. Nearly complete 1 H‐NMR assignments were obtained for the 77 amino acid residues and partial assignments for the N‐glycan and the glycosylphosphatidylinositol (GPI) anchor. These results together confirm that the C‐terminal residue of the mature protein is Asn 77 and that the urine‐derived form retains the nonlipid part of the GPI anchor. The data further indicate that the GPI anchor and possibly the N ‐glycan are structurally inhomogeneous and suggest that the phospholipid present in the intact GPI anchor was removed by phosphatidylinositol‐specific phospholipase‐D. The folding topology of the protein was determined from NOE enhancements and slowly exchanging backbone amide protons and consists primarily of five extended strands (denoted β 1 – β 5 in sequence order), arranged into separate two‐stranded ( β 1 and β 2 ) and three‐stranded ( β 3 – β 5 ) antiparallel β ‐sheets. The same folding topology is found in all of the snake venom neurotoxins whose structures have been determined. The region between the β 4 and β 5 strands has helical character, a feature that is not present in the neurotoxins but that is seen in the topologically similar wheat germ agglutinin.