Research Summary

Sickle Cell Hemoglobin
Sickle cell anemia is caused by the intracellular polymerization of sickle cell hemoglobin to form rod-like fibers. A knowledge of the fiber structure could be used for the design of an agent that could block fiber formation. We have combined the structure of hemoglobin (known from X-ray crystallography) and the molecular coordinates of the fiber (determined from electron microscopy) in order to synthesize a model which shows the intermolecular contacts of the fiber. This approach has allowed us to determine the contacts which form between molecules in the fiber. We are now studying how various mutations (some obtained by site directed mutagenesis) affect fiber structure. Such studies are expected to account for the structural and chemical properties of fibers in terms of intermolecular interactions.

Human Erythrocyte Membrane Skeletons
Red cells are able to elastically deform. The extraordinary importance of this property can be appreciated from recalling that, although the human red cell is a biconcave disk eight microns in diameter, it can easily pass through capillaries half this size. This remarkable feat is accomplished by the red cell transiently changing its shape during passage after which its well-known biconcave form spontaneously and nearly instantly recovers. We are studying the structural basis of this property using cryo electron microscopy.

Acetylcholine Receptors
The acetylcholine receptor is responsible for transduction of the nerve impulse to muscular contraction. The receptor lies at the neuromuscular junction in the muscle membrane. It has five subunits denoted as a1,a2,b,d,g. Current work in our lab involves labeling different subunits with monoclonal antibodies against defined defined sequences in order to determine the subunit arrangement (which appears to still be a matter of debate in spite of the considerable work done in other labs). We are using two dimensional crystalline tubes in order to determine the location of the labels.

Selected Publications

Turner, M. S., Briehl, R. W., Ferrone, F. A. and Josephs, R. (2003). "Twisted protein aggregates and disease: the stability of sickle hemoglobin fibers." Phys Rev Lett 90: 128103. (PubMed)

Turner, M.S., Ferrone, F. A., Briehl, R. W., and Josephs, R. (2002). Anisotropy in Sickle Hemoglobin Fibers from Fluctuations in Fiber Bending and Twist. Biophysical J. 82:504a

Wang, J. C., Turner, M. S., Agarwal, G., Kwong, S., Josephs, R., Ferrone, F. A. and Briehl, R. W. (2002). "Micromechanics of isolated sickle cell hemoglobin fibers: bending moduli and persistence lengths." J Mol Biol 315: 601-12. (PubMed)

Agarwal, G., Wang, J. C., Kwong, S., Cohen, S. M., Ferrone, F. A., Josephs, R. and Briehl, R. W. (2002). "Sickle hemoglobin fibers: mechanisms of depolymerization." J Mol Biol 322: 395-412. (PubMed)

Li, X., Briehl, R. W., Bookchin, R. M., Josephs, R., Wei, B., Manning, J. M. and Ferrone, F. A. (2002). "Sickle hemoglobin polymer stability probed by triple and quadruple mutant hybrids." J Biol Chem 277: 13479-87. (PubMed)

Nooney, R., Dhanasekaran, T., Chen, Y., Josephs, R., Ostafin, A. (2002). Controlling Mesoporous Silicate Nanoparticle Size with Co-solvent. Chemistry of Materials 14:4721-28

Nooney, R.I., Dhanasekaran, T., Chen, Y., Josephs, R. and Ostafin, A. (2002). Self-assembled highly ordered spherical mesoporous silica/gold nanocomposites. A.E. Adv. Mater. 14(7): 529-532.