Proteomics of M-L antigens modulating cation transport

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DESCRIPTION (provided by applicant): The proposed project entails the use of new technological approaches to elucidate the biochemical nature of the M/L membrane blood group antigens. These sheep red blood cell (SRBC) proteins are functionally associated with the Na/K pump and K-CI cotransporter (COT). In SRBCs with low potassium (Ki) and high sodium (Nai) levels, a dominant genetic trait, Ki inhibits the Na/K pump causing the low Ki (LK) high Nai steady state levels. LK SRBCs possess two functionally separable L antigens, Lp and Li. AIIo-immune L antisera stimulate the Na/K pump several-fold due to the Lp- and inhibit K-CI COT by more than 60% due to the Li-antigen/antibody reactions. Thus, Lp is an inhibitor of the Na/K pump and Li an activator of K-CI COT. High Ki (HK) SRBC with a normal Na/K pump and low K-CI COT has M antigens not functionally associated with either transporter. The hypothesis is that Lp and Li, modulate Na/K pump and K-CI COT via signal transduction pathways, where one rate limiting step may be controlled by the LK gene. To understand the biochemistry of these antigens fully, the following strategies will be taken: 1. Preparation of high purity, highly functional Lp, Li and M antibodies from polyclonal L and M antisera by affinity chromatography on LK and HK SRBC membrane ghosts covalently immobilized on CNBr-activated Sepharose. 2. Biosensor-based interaction analysis to establish kinetic binding events between M and L antigen positive HK and LK SRBC ghosts, respectively, and their respectively immobilized affinity-purified L and M antibodies. Optimization of conditions relevant to the stabilization of immune complexes, and conversely determination of conditions useful for destabilizing immune complexes. 3. Use of affinity-purified L and M antibodies for i) antigen pull-down experiments on alkali-stripped, detergent-soluble, intrinsic membrane proteins, and ii) M and L epitope excision experiments on intact SRBC ghosts. 4. Mass fingerprinting and sequencing of L and M tryptic peptides followed by protein identification through database and Blast searches. 5. Functional proteomics by heterologous expression systems and verification of the identity of the L antigens by reversal of anti-Lp mediated Na/K pump stimulation and the anti-Li inhibition of K-CI COT by Rb influx measurements, and detection of the M antigen by inhibition of anti-M mediated immune hemolysis. Given the ubiquitous presence of the Na/K pump and K-CI COT in all mammalian cells, the molecular identification of the L and M antigens will explain the molecular basis of the HK/LK dimorphism and the regulation of these ion transporters and will potentially reveal a molecular basis for diseases where changes in ion transport do not correlate with either functional mutations or alterations in protein expression levels.