Mapping of glycolytic enzyme-binding sites on human erythrocyte band 3.
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ABSTRACT:
SUBMITTER: Chu H
PROVIDER: S-EPMC1635443 | biostudies-other | 2006 Nov
REPOSITORIES: biostudies-other
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Project description:To characterize the location of glycolytic enzymes (GEs) in intact human erythrocytes, freshly drawn blood was fixed and stained with Abs to GAPDH, aldolase, phosphofructokinase (PFK), pyruvate kinase (PK), lactate dehydrogenase (LDH), carbonic anhydrase II, Hb, and band 3 (AE1). Confocal microscopy revealed that in cells where band 3 displays its expected membrane staining and Hb is evenly distributed across the cytoplasm, GEs are largely limited to the membrane. Biochemical studies confirmed that the membrane binding sites for GAPDH, aldolase, and PFK reside on band 3, but related analyses demonstrate that sites for PK and LDH do not. Four lines of evidence demonstrate that the GEs are at least partially assembled into multimeric complexes near the NH2 terminus of band 3. First, a mAb to residues 1-12 of band 3 displaces all of the above GEs from the membrane, including LDH and PK, which do not bind band 3. Second, tyrosine phosphorylation of the NH2 terminus of band 3 (Y8 and Y21) reversibly releases all of the GEs from the membrane, including LDH and PK. Third, deoxygenation of RBCs dislodges all GEs from the membrane, consistent with the established ability of deoxyHb but not oxyHb to bind the NH2 terminus of band 3. Fourth, a large increase in the accessibility of enzyme epitopes is observed upon dissociation of GEs from the membrane. We conclude, therefore, that GEs are organized into complexes on the membrane whose assembly is regulated by oxygenation and phosphorylation.
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Project description:Evidence accumulated over the years suggests that human erythrocyte membrane protein 4.2 is one of the proteins involved in strengthening the cytoskeleton-membrane interactions in the red blood cell. Deficiency of protein 4.2 is linked with a variety of hereditary haemolytic anaemia. However, the interactions of protein 4.2 with other proteins of the erythrocyte membrane remain poorly understood. The major membrane-binding site for protein 4.2 resides on the cytoplasmic domain of band 3 (CDB3). In order to carry out an initial characterization of its interaction with the CDB3, protein 4. 2 was subjected to proteolytic cleavage and gel renaturation assay, and the 23-kDa N-terminal domain was found to interact with band 3. This domain contained two putative palmitoylatable cysteine residues, of which cysteine 203 was identified as the palmitoylatable cysteine. Recombinant glutathione S-transferase-fusion peptides derived from this domain were characterized with respect to their ability to interact with the CDB3. Whereas these studies do not rule out the involvement of other subsites on protein 4.2 in interaction with the CDB3, the evidence suggests that the region encompassing amino acid residues 187-211 is one of the domains critical for the protein 4.2-CDB3 interaction. This is also the first demonstration that palmitoylation serves as a positive modulator of this interaction.
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Project description:Protein 4.2 is a major component of the red blood cell membrane skeleton. Deficiency of protein 4.2 is linked with a variety of hereditary haemolytic anaemias. However, the interactions of protein 4.2 with other proteins of the erythrocyte membrane remain poorly understood. The major membrane-binding site for protein 4.2 resides on the cytoplasmic domain of band 3. Protein 4.2 interacts directly with spectrin in solution, suggesting that it stabilizes interactions between the membrane skeleton and the erythrocyte membrane. A 30 kDa polypeptide, with its N-terminus corresponding to amino acid residue 269, derived by partial proteolysis of protein 4.2, was found to interact with biotinylated spectrin in gel renaturation assays. A series of overlapping glutathione S-transferase fusion peptides were constructed, and an alpha-helical domain encompassing residues 470-492 was found to be instrumental in mediating protein 4.2-spectrin interactions. Direct binding of a synthetic peptide, with the sequence corresponding to residues 470-492, to spectrin and the ability of the peptide to inhibit spectrin binding of protein 4.2 confirmed that these residues are crucial in mediating protein 4.2-spectrin interactions.
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