The Protein Code
Understanding the proteins encoded by the genome and interpreting their behaviour within human cells will be important in developing more detailed knowledge of what is happening in diseased cells. It is the many types of protein molecules that actually do most of the work in cells. Professor Angus Lamond of the University of Dundee, together with his collaborator, Professor Matthias Mann at the University of Southern Denmark in Odense are advancing our understanding of the dynamic processes that take place within human cells…
Professor Angus Lamond of the University of Dundee, together with his collaborator, Professor Matthias Mann at the University of Southern Denmark in Odense are advancing our understanding of the dynamic processes that take place within human cells. The focus of their research is on proteins and the proteome (see italicised explanations). Working with their international teams, Professors Lamond and Mann are using new techniques to study in unprecedented detail how proteins move inside human cancer cells.
Biologists have known for many years that the cells of animals and plants have a complex internal structure that is subdivided into specialised compartments, termed "organelles". It was also understood that many types of protein molecules could move between these different compartments within the cell. However, knowing exactly which proteins move under which conditions has proved difficult to measure in detail and even harder to quantify.
The Lamond and Mann groups have pioneered the combined use of mass spectrometry, stable isotope labelling of human cells grown in culture and time-lapse fluorescence microscopy to characterise how the levels of hundreds of different human proteins change over time within organelles under different cell growth conditions. The location of proteins also changes over time and these new techniques allow snap shots to reveal the changes as they occur. Lamond refers to this as "time-lapse proteomics".
"The results we have obtained using our new ‘Time-Lapse Proteomics’ approach have shown just how dynamic and extensive protein movements between subcellular compartments can be," says Professor Lamond. "We didn’t expect the flux to be so dramatic and to involve so many proteins moving in such a complex fashion.
The ‘Time-Lapse Proteomics’ studies described here rely upon a procedure to repeatedly identify and measure the levels of each protein within a specific cell compartment. To do this, cultures of human cells are grown in the laboratory in media containing different chemical isotopes that label the proteins in each culture by changing their mass. The separate cultures are then treated differentially with specific drugs and the compartment under study biochemically purified from the cells. The proteins in the compartment are identified using a mass spectrometer - an instrument that can separate and measure molecules based on their mass. Because the proteins from each culture are labelled with isotopes that subtly change their mass, the mass spectrometer allows the relative levels of each type of protein in the organelle to be compared.
Now that we have a way to measure these changes accurately for hundreds of proteins in a single experiment, we aim to build a detailed picture of the changes that can occur in diseased cells."
Lamond comments on the work at his lab: "Using high sensitivity mass spectrometry techniques, we have so far identified around 700 human proteins in the cellular organelle called the nucleolus. We determined the kinetics of over 400 nucleolar proteins after exposing cells to various drug treatments and thereby demonstrated that there is no unique, complete proteome for the nucleolus, but rather an overlapping set of proteomes that are relevant to different cell states or conditions."
This ground-breaking work demonstrates how biologists are recruiting new technologies and working across disciplines to advance our understanding of the human genome and its protein products. It should provide valuable new insights in the future into the molecular mechanisms involved in a range of human diseases.
Further details on the latest results from the Lamond and Mann groups can be viewed online at www.lamondlab.com/f7proteomics.htm