A biochemical study of the interactions of protein 4.1 with the human erythrocyte membrane and associated cytoskeletal components

At 250,000 copies per cell, protein 4.1 is considered to be one of the major membrane skeletal proteins in the red blood cell. Early in vitro studies showed that protein 4.1 can form a dense polymeric complex with spectrin and actin filaments, and subsequent recombinant and mutational studies have mapped this activity to reside in a small central 10 kDa domain. This work demonstrates that protein 4.1 also plays an important bridging function to anchor the spectrin-actin based membrane skeleton to the membrane. In addition, experiments demonstrate that the anchoring site involved lies exclusively on transmembrane protein glycophorin C. Lastly, protein 4.1\u27s binding to erythrocyte membranes is shown to be specifically affected by IP$\sb3$ ligands. This provides initial evidence that protein 4.1 may be involved in regulatory pathways that effect PIP$\sb2$ pools in the erythrocyte membrane. A novel purification protocol is also described herein which has allowed for more time-intensive binding experiments with protein 4.1