Research projects

Research in our lab is focused on three main directions:

Single Transporter Activity Recordings (STARs). 

In a breakthrough paper in Science [1] we developed a method that resolved ionic currents with a million-fold higher sensitivity than the Nobel prize awarded method of patch clamp (atto-amperes). This allowed us to observe for the first time the function of single transporters, revealing the existence of functional heterogeneity based on hitherto unknown off-cycle states (i.e. ultra-stable inactive and leaky states with lifetimes 10^5-fold longer than those of states in the classical transport cycle). The dramatic consequence of this unforeseen complexity is that many fundamental mechanistic tenets that were based on macroscopic experiments of transport will have to be revised. This truly transformative innovation is the crowning achievement of a decade of research in our lab[2,3] and we believe is likely to spark off a technological and conceptual paradigm shift in the transport field.

Membrane curvature.

Eukaryotic life is defined by the existence of intracellular membrane-bound organelles. Endomembranes are overall more curved than the plasma membrane their heterogeneous geometrical shapes however are not arbitrary, on the contrary they are so characteristic that they have become a hallmark of the different eukaryotic organelles.[4] To elucidate why this phenotype is so remarkably conserved we have pioneered several high-throughput nanoscopic methods to study how membrane curvature is affecting the function(s) of membranes and membrane proteins, with an emphasis on Ras and G protein coupled receptors.[5-7] Our contributions have overall helped establish the notion that the properties of biological membranes are defined equally by their lipid composition and their geometrical shape.[4]

Nanoscopic heterogeneity of biological membranes. 

Spatiotemporal compositional and functional heterogeneities are a hallmark of biological membranes. We are investigating the implications of these heterogeneities for biological function and also exploit them for technological applications. For example, with high-throughput single proteoliposome measurements we quantified the composition of single proteoliposomes revealing dramatic heterogeneities.[8] As we showed, compositional heterogeneities can severely skew ensemble-average proteoliposome measurements however, if averaging is avoided such heterogeneities can be exploited to enable high-content screens that enable a dramatic reduction in protein consumption (~billion-fold) as compared to conventional assays.[8] We are currently extending this project to investigate nanoscopic compositional and functional heterogeneities of G protein coupled receptors in live cells.

 References

1. Science, 2016. 351 (6280): p. 1469-1473        
   Direct observation of proton pumping by a eukaryotic P-type ATPase 
   Salome Veshaguri, Sune M. Christensen, Gerdi C. Kemmer, Mads P. Møller, Garima Ghale, Christina Lohr, Andreas L.Christensen, Bo H. Justesen, Ida L. Jørgensen, Jürgen Schiller, Nikos S. Hatzakis, Michael Grabe, Thomas Günther Pomorski, Dimitrios Stamou                  

2. Proceedings of the National Academy of Sciences. 2009. 106 (30): p. 12341
   Quantification of nano-scale intermembrane contact areas using fluorescence resonance energy transfer.                 
   Poul Martin Bendix, M. S. Pedersen and Dimitrios Stamou.

3. Nature Nanotechnology, 2012. 7 (1): p. 51–55                   
   Mixing sub-attolitre volumes in a quantitative and highly parallel manner with soft matter nanofluidics.          
   S. M. Christensen; P.Y. Bolinger; N.S. Hatzakis; M.W. Mortensen and Dimitrios Stamou

4. Nature Chemical Biology, 2015. 11 (11): p. 822-825          
   Membrane curvature bends the laws of physics and chemistry
   Lars Iversen, Signe Mathiasen, Jannik Bruun Larsen, Dimitrios Stamou

5. Nature Chemical Biology, 2009. 5 (11): p. 835                   
   How Curved Membranes Recognize Amphipathic Helices and Protein Anchoring Motifs.                   
   N. S. Hatzakis, V. K. Bhatia, J. Larsen, K. L. Madsen, P. Y. Bolinger, A. H. Kunding, J. Castillo, U. Gether, P. Hedegård and Dimitrios Stamou.

6. Nature Chemical Biology, 2015. 11 (3): p. 192-194            
   Front Cover Page 
   Membrane curvature enables N-Ras lipid anchor sorting to liquid-ordered membrane phases
   Jannik Bruun Larsen, Martin Borch Jensen, Vikram K. Bhatia, Søren L. Pedersen, Thomas Bjørnholm, Lars Iversen, Mark Uline, Igal Szleifer, Knud J. Jensen, Nikos S. Hatzakis and Dimitrios Stamou

7. Nature Chemical Biology, 2017. 13: p. 724-729.
   Front Cover Page
   Membrane curvature regulates sorting of GPCRs within the plasma membrane of living cells in a ligand-specific manner
   Kadla R. Rosholm, Natascha Leijnse, Anna Mantsiou, Vadym Tkach, Søren L. Pedersen, Volker F. Wirth, Lene B. Oddershede, Knud J. Jensen, Karen L. Martinez, Nikos S. Hatzakis, Poul Martin Bendix, Andrew Callan-Jones and Dimitrios Stamou

8. Nature Methods, 2014. 11 (9): p. 931-934     
   Nanoscale high content analysis using compositional heterogeneities of single proteoliposomes
   Signe Mathiasen, Sune M. Christensen,, Juan Jose Fung, Soren G. F. Rasmussen, Jonathan F. Fay, Sune K. Joergensen, Salome Veshaguri, David L. Farrens, Maria Byrne, Brian Kobilka, Dimitrios Stamou