CD59; CD59 glycoprotein; membrane attack complex inhibition factor; MACIF; MAC-inhibitory protein; MAC-IP; protectin; MEM43 antigen; membrane inhibitor of reactive lysis; MIRL; 20 kD homologous restriction factor; HRF-20; HRF20; 1F5 antigen (MIC11, MIN1, MIN2, MIN3, MSK21)

^[1]^[2]^[3]^[4]^[5]

Function

associates with/activates lck^[1]
regulates complement mediated cell lysis by inhibiting formation of membrane attack complex (MAC)
expression on erythrocytes important for survival
acts by binding to the C8 &/or C9 complements of the assembling MAC, thus preventing incorporation of the multiple copies of C9 required for complete formation of the osmolytic pore
this inhibitor appears to be species-specific
involved in signal transduction for T-cell activation complexed to a protein tyrosine kinase
interacts with T-cell surface antigen CD2

N- & O-glycosylated
the N-glycosylation mainly consists of a family of biantennary complex-type structures with & without lactosamine extensions & outer arm fucose residues
also significant amounts of triantennary complexes (22%)
variable sialylation also present in the Asn-43 oligosaccharide
predominant O-glycans are mono-sialylated forms of the disaccharide, gal-beta-1,3galNAc; their sites of attachment are probably on Thr-76 & Thr-77
the GPI-anchor of soluble urinary CD59 has no inositol-associated phospholipid, but is composed of seven different GPI-anchor variants of one or more monosaccharide units
major variants contain sialic acid, mannose & glucosamine
contains 1 UPAR/Ly6 domain

defects, if together with CD55 defects, associated with paroxysmal nocturnal hemoglobinuria
glycation is found in diabetic subjects, but only at minimal levels in nondiabetic subjects
glycated CD59 lacks MAC-inhibitory function & confers to vascular complications of diabetes

the soluble form from urine retains its specific complement binding activity, but exhibits greatly diminished ability to inhibit MAC assembly on cell membranes