Uwe Sauer Lab

We aim to understand the underlying mechanisms of the way large protein complexes are assembled and maintained, such as the photosystem II in plant cells. We also investigate the activity of different enzymes (e.g. ATPases and GTPases) and how structural conformational changes are triggered by the hydrolysis of the substrate.

Proteins in photosystem II

Photosynthesis is arguably the most important biochemical process on Earth. It is the process behind our food production and contributes to large parts to our heat and energy needs. As a byproduct, photosynthesis provides the oxygen we breathe. Plants, algae and cyanobacteria are able to transform light energy, carbon dioxide and water into storable chemical energy and oxygen. A few large protein complexes, embedded in the thylakoid membranes of oxygenic organisms, are of particular interest. The research in my group focuses on photosystem II (PSII) and in particular on proteins that are involved in the assembly, maintenance and repair of PSII, but are not part of the final complex. We have determined the structures of three of these “assisting proteins”, HCF136, LPA19 and MPH2 from Arabidopsis thaliana and study them biochemically and through mutations. We will use an in vitro plant cell suspension system where the production of PSII can be chemically synchronized to produce PSII at different stages of assembly and analyze the premature PSII complexes with powerful electron microscopy methods and X-ray diffraction methods available at Umeå University. In addition, we use bioinformatics approaches to study PS II assembly factors from different organisms, which will provide important insights into their evolutionary relationships and development from primitive organisms such as cyanobacteria to sophisticated higher plants. 

Molecular mechanisms of bacteria

The objective of this project is to understand the molecular mechanisms by which bacteria sense harmful aromatic compounds, which they can break down and use as carbon sources. A key regulator is DmpR, which regulates the dmp-operone in a (methyl)phenolic-dependent manner in Pseudomonas putida CF600. DmpR belongs to a family of transcriptional activators that use ATP hydrolysis to initiate binding to s54-RNA polymerase. The sensing and binding of phenolic effector compounds and ATP triggers a conformation change in DmpR, which converts the protein from its inactive dimeric form to an active hexamer, thus enabling transcription of genes coding for specialized catabolic enzymes.

We have determined the 1.5 Å resolution crystal structure of the central AAA+ domain of DmpR, which hydrolyses ATP and interacts with the  s54-RNA polymerase. The structure revealed that tyrosine residue 233 prevents ATP from proper binding at the active site and thus inhibits hydrolysis and transition to the active hexamer. Structural analysis of a mutated variant of DmpR where Tyr233 was replaced by alanine (Tyr233-Ala) revealed that the adjacent Tyr234 flipps into the nucleotide-binding pocket, thus replacing Tyr233 and restoring the steric hindrance that prevents ATP from binding. Analysis of the activities of wild-type and alanine substituted DmpR proteins suggest that these observed structural features have important consequences for DmpR’s ATPase and transcriptional activities. Based on our findings, we have proposed a model where effector binding displaces Tyr233 thus allowing correct binding of ATP which leads to hexamerization and ultimately transcriptional activation.

Infrastructure Protein Expertise Platform (PEP)

Uwe Sauer also leads the Protein Expertise Platform (PEP), which is part of Protein Production Sweden (PPS), a national infrastructure that receives funding from the Swedish Research Council (VR) and the local node universities.