Structure of a soluble, glycosylated form of the human complement regulatory protein CD59.
BACKGROUND
CD59 is a cell-surface glycoprotein that protects host cells from complement-mediated lysis by binding to and preventing the normal functioning of the complement proteins C8 and/or C9 which form part of a membrane penetrating assembly called the membrane attack complex. CD59 has no structural similarity to other complement proteins, but is an example of a plasma protein domain type found also in murine Ly-6 proteins and the urokinase-type plasminogen activator receptor.


RESULTS
CD59 was purified from human urine, retaining the N-glycan and at least some of the non-lipid component of the glycosylphosphatidylinositol membrane anchor. The three-dimensional structure of the protein component has been determined in the presence of the carbohydrate groups using two-dimensional NMR spectroscopy. The protein structure is well defined by the NMR data (root mean square deviation from the mean structure of 0.65 A for backbone atoms and no distance constraint violations greater than 0.4 A). Structure calculations were also carried out to model the orientation of the N-acetylglucosamine residue that is directly linked to Asn18.


CONCLUSIONS
The main features of the protein structure are two antiparallel beta-sheets (a central one with three strands and another with two), a short helix that packs against the three-stranded beta-sheet, and a carboxy-terminal region that, although lacking regular secondary structure, is well defined and packs against the three-stranded beta-sheet, on the opposite face to the helix. We have used the structure, in combination with existing biochemical data, to identify residues that may be involved in C8 binding.
Fletcher
C M
CM
MRC Laboratory of Molecular Biology, Cambridge, UK.
Harrison
R A
RA
Lachmann
P J
PJ
Neuhaus
D
D
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry* / Q000302:isolation & purification / Q000652:urine; D018957:CD59 Antigens; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D003169:Complement Inactivator Proteins / Q000737:chemistry*; D004220:Disulfides / Q000032:analysis; D006031:Glycosylation; D017261:Glycosylphosphatidylinositols / Q000032:analysis; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000302:isolation & purification / Q000652:urine; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000032:analysis / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid
D015703:Antigens, CD; D018957:CD59 Antigens; D003169:Complement Inactivator Proteins; D004220:Disulfides; D017261:Glycosylphosphatidylinositols; D008562:Membrane Glycoproteins; D009844:Oligosaccharides