Structural and immunological studies of GPI-anchored brush border hydrolases

The complement of brush border hydrolases provides an excellent model system for study of the structure, topology and assembly of plasma membrane proteins. Among the peptidases of the renal brush border are a number of glycosylphosphatidylinositol (GPI)-anchored proteins, especially membrane dipeptidase and aminopeptidase P. Affinity purification protocols have led to the isolation of homogeneous forms of these proteins and membrane dipeptidase has been cloned and expressed in Xenopus oocytes and Cos-1 cells. The core glycan structures of both human and porcine dipeptidase have been determined, allowing direct comparisons of the GPI anchors on the same protein in different species. Aminopeptidase P has been compared in the brush borders of pig kidney and intestine and may well be anchored in distinct ways in the two tissues. Immunological cross-reactivity of polyclonal antibodies to these two proteins has revealed the phospholipase C-cleaved GPI anchor as the common epitope and defined those components of the anchor important for recognition. These antibodies are also proving useful in characterizing GPI-derived mediators that may be involved in cell signalling processes. These abundant ectopeptidases offer a number of advantages for studies of the biochemistry of mammalian GPI anchors

Correlation between antibodies to mannophosphoinositides & detection of antigen in circulating immune complexes in patients with pulmonary tuberculosis.

Enzyme linked immunosorbent assays were used to detect the concentration of mannophosphoinositides in circulating immune complexes (CICs) and antibodies to these antigens in the sera of patients with pulmonary tuberculosis. Serum samples from 235 tuberculosis patients at various levels of disease progression were analysed. Multiple regression analysis showed a direct correlation between antigen levels in CICs and serum antibodies to mannophosphoinositides.