Faculty Research
Alphabetical · By research area

Research in our group is focused on understanding intermolecular interactions in biological membranes. We study the dynamics and distribution of molecules within the membrane as a means of understanding their function in events such as cell-cell communication, signal transduction, adhesion and locomotion of cells and breathing. There are four major themes:

1. Studies of the distribution and extent of aggregation and interaction of membrane receptors in living cells. This work is based on analysis of laser scanning confocal microscopy images (Fig 1A) to estimate the density of protein clusters and their sizes. We have developed specific tools - Image Correlation Spectroscopy (Fig 1B) and Image Cross-correlation Spectroscopy for this purpose. There are three sub-themes:

1. the function of growth factor receptors and their interaction with cellular substructures
2. the effect of receptor function on assembly of coated pits and caveolae
3. the interaction of GPI anchored proteins with lipid rafts

Figure 1: Receptor Distribution (A) and the corresponding correlation function (B)

2. Studies of the dynamics of movement of molecules and clusters in living cells. This work applies fluorescence photobleaching, fluorescence correlation spectroscopy and dynamic image correlation spectroscopy (Fig 2) to study the diffusion and flow of individual molecules or complexes on the surface or within the cell. This provides detailed information of which molecules interact and how the dynamics relates to their function

Figure 2: Decay of correlation function amplitude reveals rate of movement

3. Studies of the mechanical properties of adhering cells. This work utilizes combinations of modern imaging tools such as confocal microscopy, atomic force microscopy (Fig 3A), near-field scanning optical microscopy and interfacial force microscopy to study the mechanical properties of cell structures of known biochemistry. The purpose is to understand the forces that give cells shape and allow them to adhere (Fig 3B) and move.

Figure 3: Measurement of adhesion forces between Fibronectin and integrin analogs

4. Studies of lung surfactants from healthy and dysfunctional animals. The purpose is to understand how the particular lipids and proteins present in lung surfactants affect the function and malfunction of the surfactant films in lungs. The objective is to establish the phase behaviour of the systems (Fig 4A), to identify the composition and physical characteristics of different phases (Fig 4B) and to establish the mechanism whereby these components create a low surface tension environment dynamically. The program combines imaging by fluorescence, atomic force microscopy (Fig 4A) and secondary ion mass spectrometry (Fig 4B).

Figure 4: Distribution of solid phases of DPPC in a liquid phase (A) and the distribution of deuterated palmitic acid from DOPC in a monolayer detected by TOF-SIMS in a mixture (B) confirm that DOPC is in the liquid phase only

Selected Publications

E. Keating, C.M. Brown and N.O. Petersen, "Mapping Molecular Interactions and Transport in Cell Membranes by Image Correlation Spectroscopy" Chapter 16 in Molecular Imaging: FRET Microscopy and Spectroscopy Edited by Pariasamy and Day, Oxford University Press, June 2005.

A. Nohe and Nils O. Petersen "Analyzing Protein-Protein Interactions in Cell Membranes" Bioessays 2004, 26, 196-203.

A. Nohe, E. Keating, T.M. Underhill, P. Knauss and N.O. Petersen, "Effect of the Distribution and Clustering of BMP Receptors on the Activation of Signaling Pathways" J. Cell Science 2003, 116, 3277-3284.

R.R. Harbottle, K. Nag, N.S. McIntyre, F. Possmayer and N.O. Petersen, "Molecular Organization in Bovine Pulmonary Surfactant Films Revealed by Time-of-Flight Secondary Ion Mass Spectrometry" Langmuir 2003, 19, 3698-3704.

C.L. Lee, M. Revington, S.D. Dunn and N.O. Petersen "The Lateral Diffusion of Selectively Aggregated Peptides in Giant Unilamellar Vesicles" Biophysical Journal 2003, 84,1756-64. See also Correction in Biophysical Journal 2003, 85, 1338.