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Karlsson group research

NMR and protein-protein interactions

Many biological processes depend critically on transient interactions between proteins or between proteins and DNA/RNA. Despite this, only a small fraction of data base structures represent complexes, let alone structures of transient complexes. X-ray crystallography, an otherwise extremely powerful method for solving structures of biological molecules, is of limited use for short-lived complexes, both since the crystallization process is hampered but also because crystal contacts may distort the physiologically relevant complex. Studies of dynamic assemblies, however, can readily be performed with nuclear magnetic resonance (NMR) spectroscopy.

Chemical shift mapping techniques provide information about which residues are in physical contact, but not about the relative orientation of the two proteins. NOE-based methods, which make use of the nuclear-nuclear dipole relaxation, can provide short-range distance restraints across the protein interface, but the slow build-up of the NOE makes this approach suitable only for sufficiently long-lived complexes. A paramagnetic center, on the other hand, may provide information about the relative orientation of transiently interacting proteins, and the very fast electron-nuclear dipolar relaxation makes this approach tractable also for highly transient complexes. This was demonstrated in our work on the plastocyanin-cytochrome f complex. Few natural systems contain suitably located metal binding sites, though, and instead paramagnetic spin labels may be used to obtain the wanted information. In order to extend existing methodology, we use the paramagnetic relaxation enhancement (PRE) originating from the strong dipole-dipole interaction between a proton and an unpaired electron, introduced via site-directed spin labeling (SDSL), to retrieve distance restraints across the interface of a large short-lived protein-protein complex. The methodology is applied to soluble domains, but will also be used in the characterization of soluble domains with integral membrane proteins, e.g. E. coli transhydrogenase.

Picture of Goran Karlsson

Contact Information

B. Göran Karlsson

+46 (0)31 786 3881 (Director Göran Karlsson)

+46 (0)31 786 3880

More information


Page Manager: Anders Pedersen|Last update: 6/21/2010

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