Dr Pauline Bennett
- BSc University of Sussex
- MSc McMaster University
- PhD University of London
Coming from a physics background into the Biophysics Department at King’s College, I learnt from very knowledgeable experts how to use the transmission electron microscope and analyse the resultant micrographs for insight into ordered protein arrays, especially those from muscle. I now have many years experience of a range of specimen preparation techniques for microscopy including, rapid freezing, high pressure freezing and freeze substitution. Analytical techniques include electron tomography. My present research interests lie in analysing the membrane cytoskeleton in the heart.
Throughout my career at Kings I have had a strong interest in the structure and function of muscle, particularly in the organisation of the proteins in the filaments of the contractile apparatus. Electron microscopy of muscle specimens prepared by a wide variety of techniques has enabled different aspects of the structure to be examined.
Some years ago I started collaboration with Dr Jennifer Fordham and turned my attention to heart muscle. She was an expert in the properties of the spectrin-associated membrane cytoskeleton in the red blood cell and recognised that these proteins would play a significant role in heart function. Thus began a structural analysis of the organisation of the spectrin complex and its relationship to other features of the cardiomyocytes.
The distribution of the spectrin complex in the heart
In the heart, the muscle cells have a unique morphology and organisations. The maintenance of this shape can to a large measure be attributed to the underlying membrane cytoskeleton which confers stability to the myocardium and senses and absorbs mechanical strain. In addition, it has become clear that it also plays a key role in corralling and organising other essential membrane proteins.
The spectrin-associated complex is a major component of this membrane cytoskeleton. I am interested in determining how this complex is distributed in the heart and what contribution it makes to cardiac structure and function.
Diagram of the spectrin-associated complex underlying the cell membrane
The intercalated disc and the transitional region
One aspect of the unique morphology of the myocytes is that the cells join end to end in a convoluted membrane called the intercalated disc. This is a very important region for transmitting the mechanical, electrical and chemical signals from one cell to the next.
We have become interested in the transition between the contractile fibrils in the bulk of the cell and their incorporation into the intercalated disc. Using electron tomography we can study the paths of the filaments and how they interact with other structures in the transitional junction.
Electron micrograph of a longitudinal section of the intercalated disc
The intercalated disc in disease
The intercalated disc exhibits morphological changes in dilated cardiomyopathy. One such change is an increase in the amplitude of the folds in the cell membrane. In collaboration with Dr Elisabeth Ehler, of the Cardiovascular Division, here at King’s College London and Dr Irina Agarkova in Zurich we have looked in more detail at this increase and find that it is age related in mouse models of the disease.
Protein 4.1 in normal and diseased hearts
We have a long term collaboration with Dr Anthony Baines of the University of Kent, Canterbury, on studies of spectrin associated proteins in the heart. One of these, Protein 4.1, is a multifunctional protein, essential to maintaining the spectrin-actin link in the cytoskeletal network below the membrane surface, bit also able to attach to transmembrane proteins. We find that the four isoforms of Protein 4.1 have distinct locations within the heart and two of them localise to complexes with ion channels proteins.
The heart of a genetically modified mouse which expresses a short form of Protein 4.1R, the erythrocyte form of the protein, has been investigated physiologically and mechanically in collaboration with Dr Cesare Terracciano and his colleagues at Imperial College. Differences from the normal heart in the heart beat rate, and in calcium handing indicates how important to function this protein is. Although there are no gross morphological effects, we are interested to characterise the more subtle structural changes may occur.
- Hanson, J., O'Brien, E.J. & Bennett, P. M. (1971). Structure of the myosin containing filament assembly (A-Segment) separated from frog skeletal muscle. J. Mol. Biol. 58, 865-871.
- Bennett, P. M. (1974). Decrease in section thickness on exposure to the electron beam; the use of tilted sections in estimating the amount of shrinkage. J Cell Sci. 15, 693-701.
- Moos, C., Offer, G., Starr,R. & Bennett, P. M. (1975). Interaction of C-protein with myosin, myosin rod and light meromyosin. J. Mol. Biol. 97, 1-9.
- Ungewickel, E., Bennett, P M., Calvert, R., Ohanian, V. & Gratzer, W.B. (1979). In vitro formation of a complex between cytoskeletal proteins of the human erythrocyte. Nature, 280, 811-814.
- Bennett, P. M & Elliott, A. (1981). The structure of the paramyosin core in molluscan thick filaments. J. Musc. Res. Cell Motil. 2, 65-81.
- Elliott, A. & Bennett, P. M. (1984). The molecular organisation of paramyosin in the core of the molluscan thick filament. J. Mol. Biol. 174, 477-493.
- Bennett, P. M., Craig, R.,Starr, R. & Offer, G. (1986) The ultrastructural location of C-protein, X-protein and H- protein in rabbit muscle. J. Musc. Res.Cell Motil. 7, 550-567.
- Bennett, P M & Elliott, A. (1989). The 'catch' mechanism in molluscan Muscle: an electron microscopy study of freeze-substituted anterior byssus retractor muscle of Mytilus edulis. J. Musc. Res. Cell Motil.10, 297-311.
- Hawkins, C.J. & Bennett, P.M. (1995) Evaluation of freeze substitution in rabbit skeletal muscle. Comparison of electron microscopy to x-ray diffraction. J. Musc. Res Cell Motil. 16, 303-318.31.
- Bennett, P.M. & Gautel, M. (1996) Titin domain patterns correlate with the axial disposition of myosin at the end of the thick filament. J. Molec. Biol. 256, 896-903.
- Bennett, P.M., Hodkin, T.E. & Hawkins, C. (1997) Evidence that the tandem Ig domains near the ends of the muscle thick filament form an inelastic part of the I-band titin. J. Struct. Biol. 120, 93-104.
- Bennett, P.M. (1998) Structural changes in samples cryofixed by contact with a cold metal block. J. Micros. 192, 259-268.
- Bennett, P.M., Baines, A.J., Lecomte, M-C., Maggs A.M. & Pinder, J.C. (2004) Not just a plasma membrane protein: in cardiac muscle cells alpha-II spectrin also shows a close association with myofibrils. J. Musc. Res. Cell Motil. 25, 119-126
- Bennett, P.M. (2005) Jean Hanson - a woman to emulate: leading research into the molecular basis of contractility in muscle. J Muscle Res Cell Motil. 25, 451-454.
- Bennett P.M., Maggs A.M., Baines A.J. and Jennifer C. Pinder (2006) The Transitional Junction: A New Functional Compartment at the Intercalated Disc Mol. Biol. Cell 17, 2091-2100
- Mark A. Stagg, Edward Carter, Nadia Sohrabi, Urszula Siedlecka, Gopal K. Soppa, Fiona Mead, Narla Mohandas, Pamela Taylor-Harris, Anthony Baines, Pauline Bennett, Magdi H. Yacoub, Jennifer C. Pinder and Cesare M.N. Terracciano (2008) Cytoskeletal Protein 4.1R Affects Repolarization and Regulates Calcium Handling in the Heart Circ. Res. 103;855-863
- Pradeep K. Luther, Pauline M. Bennett, Carlo Knupp, Roger Craig, Raúl Padrón, Samantha P. Harris, Jitendrakumar Patel and Richard L. Moss (2008) Understanding the Organisation and Role of Myosin Binding Protein C in Striated Muscle by Analysis of Normal and MyBP-C knockout muscle
- Baines AJ, Bennett PM, Carter EW, Terracciano C. (2009) Protein 4.1 and the control of ion channels. Blood Cells Mol Dis. Mar 7. [Epub ahead of print]