The cytoplasmic domain of band 3 serves as a center of erythrocyte membrane organization and constitutes the major substrate of erythrocyte tyrosine kinases. Tyrosine phosphorylation of band 3 is induced by several physiologic stimuli, including malaria parasite invasion, cell shrinkage, normal cell aging, and oxidant stress (thalassemias, sickle cell disease, glucose-6-phosphate dehydrogenase deficiency, etc). In an effort to characterize the biologic sequelae of band 3 tyrosine phosphorylation, we looked for changes in the polypeptide's function that accompany its phosphorylation. We report that tyrosine phosphorylation promotes dissociation of band 3 from the spectrin-actin skeleton as evidenced by: (1) a decrease in ankyrin affinity in direct binding studies, (2) an increase in detergent extractability of band 3 from ghosts, (3) a rise in band 3 cross-linkability by bis-sulfosuccinimidylsuberate, (4) significant changes in erythrocyte morphology, and (5) elevation of the rate of band 3 diffusion in intact cells. Because release of band 3 from its ankyrin and adducin linkages to the cytoskeleton can facilitate changes in multiple membrane properties, tyrosine phosphorylation of band 3 is argued to enable adaptive changes in erythrocyte biology that permit the cell to respond to the above stresses. (Blood. 2011; 117(22):5998-6006) IntroductionEarly views of the human erythrocyte argued that the cell was inert to external stimuli and that its complement of protein kinases, phospholipases, G proteins, phosphatases, and hormone receptors simply constituted nonfunctional vestiges of signaling pathways that were once operational in erythroid precursor cells. More recent evidence, however, has revealed that the human erythrocyte is highly responsive to its environment and that the cell's rich ensemble of signaling proteins likely comprise critical components in the cell's communication with its extracellular milieu. Classic hormones/signaling molecules such as prostaglandin E 2 , insulin, epinephrine, endothelin, ADP, and NO are now known to modulate erythrocyte properties in an adaptive manner, and the functional activities of many intracellular signaling intermediates have been demonstrated to regulate erythrocyte behavior. [1][2][3][4][5] One of the major targets of erythrocyte signaling appears to be the predominant membrane-spanning protein, band 3. Band 3 (AE1) catalyzes the exchange of anions (primarily HCO 3 Ϫ for Cl Ϫ ) across the erythrocyte membrane, 6 anchors the spectrin/ actin cytoskeleton to the lipid bilayer, 7 organizes and regulates a complex of glycolytic enzymes, 8,9 participates in control of erythrocyte lifespan, 10,11 nucleates several important membrane-spanning proteins, 12 and serves as a docking site for multiple peripheral membrane proteins, including protein 4.1, protein 4.2, and several kinases and phosphatases. [13][14][15][16] Not surprisingly, mutations in band 3 are frequently associated with various hemolytic diseases. 17 Perhaps because of its many important functions, band 3 is a...

The aggregation of beta-lactoglobulin (BLG) at ambient temperature was studied using turbidimetry and dynamic light scattering in the range 3.8

The aggregation of insulin near its isoelectric point and at low ionic strength was suppressed in the presence of heparin. To understand this effect, we used turbidimetry and stopped-flow to study the pH-and ionic strength (I)-dependence of the aggregation of heparin-free insulin. The results supported the role of interprotein electrostatic interactions, contrary to the commonly held view that such forces are minimized at pH ) pI. Electrostatic modeling of insulin (DelPhi) revealed that attractive interactions arise from the marked charge anisotropy of insulin near pI. We show how screening of the interprotein attractions by added salt lead to maximum aggregation near I ) 0.01 M, corresponding to a Debye length nearly equal to the diameter of the insulin dimer, consistent with a dipole-like protein charge distribution. This analysis is also consistent with suppression of aggregation by heparin, a strong polyanion that by binding to the positive domain of one protein, inhibits its interaction with the negative domain of another.

SummaryAurora A is overexpressed in majority of breast carcinomas. With the exception of BRCA1 and PHLDA1, no oncogenic Aurora A substrates are known in breast cancer. In this study, a chemical genetic approach was used to identify malignant targets of Aurora A, which revealed LIMK2 as a novel Aurora A substrate. Aurora A regulates LIMK2 kinase activity, subcellular localization and protein levels by direct phosphorylation at S283, T494 and T505. In response, LIMK2 also positively regulates the level of Aurora A, thereby engaging in a positive-feedback loop, promoting Aurora-A-mediated oncogenic pathways. Most importantly, LIMK2 ablation fully abrogates Aurora-A-mediated tumorigenesis in nude mice, suggesting that LIMK2 is a key oncogenic effector of Aurora A. Furthermore, LIMK2 ablation acts synergistically with inhibition of Aurora A in promoting cell death. Finally, Aurora-A-mediated upregulation of LIMK2 appears to be a common mechanism in many cancers. LIMK2 inhibition or ablation is therefore an alternative approach for modulating Aurora A deregulation in cancer.

Background: Erythrocyte band 3 exists in three populations; ankyrin-bound, adducin-bound, and free. Results: In wild-type murine erythrocytes, ϳ40% of band 3 is attached to ankyrin, ϳ33% is immobilized by adducin, and ϳ27% is free. Conclusion: Ankyrin-and adducin-bound band 3 can be monitored separately. Significance: This diffusion study demonstrates molecular differences between band 3 complexes and reveals structural heterogeneity within band 3 subpopulations.