Topics: 
  -Why Study Sickle Cell Disease?
  -Our Approach

Why Study Sickle Cell Disease?

Sickle cell disease has often been called a 'molecular disease' because it results from the mutation of one amino acid.  In the Mukerji lab our goal is to understand this disease on a molecular level. By studying the structure and energetics of sickle cell hemoglobin fibers, our research is directed towards understanding the mechanism of sickle cell hemoglobin fiber formation.  By gaining an understanding of fiber formation on this level, we can begin to design better and more effective agents to inhibit fiber formation and disrupt fibers.  Fiber formation lies at the root of sickle cell disease; therefore, understanding this process is inherent to understanding sickle cell disease.

At the most basic level, we are interested in understanding the forces that govern the association of proteins.  In particular, we are interested in the self-association of proteins that leads to the formation of fibrils.  Many diseases such as Alzheimer's disease and 'Mad Cow' disease result from the association or aggregation of proteins into fibrils.  Thus, much of the basic information gained from this research will be relevant towards understanding the assembly of proteins into larger structures, functional and non-functional.  Furthermore, the methodologies we develop to study sickle cell hemoglobin may be applied to the study of similar problems.

Deoxy Hb S fibers	Amyloid fibers	Prion fibers
Fig 6.1	Fig. 6.3	Fig 6.5
Fig 6.2	Fig 6.4	Fig 6.6
Fig 6.1 An electron micrograph of deoxyHb S fibers formed in the presence of dextran (12 g/dl). Fig 6.2 a, an electron micrograph of a bundle of deoxyHb S fibers formed in the presence of dextran. b, an optical diffraction pattern of the bundle. images taken from: Bookchin RM, Balazs T, Wang Z, Josephs R, Lew VL. (1999)Polymer structure and solubility of deoxyhemoglobin S in the presence of high concentrations of volume-excluding 70-kDa dextran. Effects of non-s hemoglobins and inhibitors. J Biol Chem 274(10), 6689-6697 http://www.jbc.org/cgi/content/full/274/10/6689/F3
fig. 6.3.   (Upper) Electron micrograph of fibers made of the glutamine- and asparagine-rich region of Sup35. images taken from: M. F. Perutz, J. T. Finch, J. Berriman, and A. Lesk(2002) Amyloid fibers are water-filled nanotubes. Proc. Natl. Acad. Sci. USA, Vol. 99, Issue 8, 5591-5595, April 16, 2002
Fig. 6.4 Scanning electron micrograph of a classical amyloid plaque (AP) of a 23-month-old Tg2576 mouse brain images taken from: G.Y. Wen, S.Y. Yang, W. Kaczmarski, X. Y. He and K. S. Pappas Presence of hydroxysteroid dehydrogenase type 10 in amyloid plaques (APs) of Hsiao's APP-Sw transgenic mouse brains, but absence in APs of Alzheimer's disease brains. Brain Res. 2002 Nov 1; 954(1):115-22.
Fig 6.5  Unusual protein structures caused by: prion-like particles in yeast images taken from: http://www.nigms.nih.gov/news/images/yeast.jpg(Copyright 1997, Cell Press)
Fig 6.6 Prion protein fibers images taken from:  Brown, D. R., Schmidt, B. and Kretzschmar, H. A (1996) Role of microglia and host prion protein in neurotoxicity of a prion protein fragment. Nature 380, 345-347

Our approach

We primarily study sickle cell fiber formation using spectroscopic methods.  X-ray crystallography has given us much information regarding the atomic structure of sickle cell hemoglobin and provided important clues regarding the association of individual molecules into fibers.  These data coupled with electron microscopy methods provide a framework for the structure of the fibers.  Interestingly, in the crystals the fibers are linear, but in solution the fibers exhibit a helical twist.  With the spectroscopic techniques that we are using in the laboratory, we can now study the fibers as they form and elucidate structural details in solution.  We have also been investigating different agents that inhibit fiber formation and how it is done.