Biology subjects

Braun, H.-P.

Publications and source records attributed to Braun, H.-P..

5 recordsLinked to original sources

bioRxiv2022

Defining the lipidome of Arabidopsis leaf mitochondria: Specific lipid complement and lipid biosynthesis capacity

Mitochondria are often considered the power stations of the cell, playing critical roles in various biological processes such as cellular respiration, photosynthesis, stress responses and programmed cell death. To maintain the structural and functional integrities of mitochondria, it is crucial to achieve a defined membrane lipid composition between different lipid classes wherein specific proportions of individual lipid species are present. Although mitochondria are capable of self-synthesizing a few lipid classes, many phospholipids are synthesized in the endoplasmic reticulum and transferred to mitochondria via membrane contact sites, as mitochondria are excluded from the vesicular transportation pathway. However, knowledge on the capability of lipid biosynthesis in mitochondria and the precise mechanism of maintaining the homeostasis of mitochondrial lipids is still scarce. Here we describe the lipidome of mitochondria isolated from Arabidopsis leaves, including the molecular species of glycerolipids, sphingolipids and sterols to depict the lipid landscape of mitochondrial membranes. In addition, we define proteins involved in lipid metabolism by proteomic analysis and compare our data with mitochondria from cell cultures since they still serve as model system. Proteins putatively localized to the membrane contact sites are proposed based on the proteomic results and online databases. Collectively, our results suggest that leaf mitochondria are capable - with the assistance of membrane contact site-localised proteins - of generating several lipid classes including phosphatidylethanolamines, cardiolipins, diacylgalactosylglycerols and free sterols. We anticipate our work to be a foundation to further investigate the functional roles of lipids and their involvement in biochemical reactions in plant mitochondria. One sentence summaryThe lipid landscape of plant mitochondria suggests that they are capable in generating several phospholipid classes with the assistant of membrane contact site-localized proteins.

plant biology↗

bioRxiv2020

CEDAR, an online resource for the reporting and exploration of complexome profiling data

Complexome profiling is an emerging omics approach that systematically interrogates the composition of protein complexes (the complexome) of a sample, by combining biochemical separation of native protein complexes with mass-spectrometry based quantitation proteomics. The resulting fractionation profiles hold comprehensive information on the abundance and composition of the complexome, and have a high potential for reuse by experimental and computational researchers. However, the lack of a central resource that provides access to these data, reported with adequate descriptions and an analysis tool, has limited their reuse. Therefore, we established the ComplexomE profiling DAta Resource (CEDAR, www3.cmbi.umcn.nl/cedar/), an openly accessible database for depositing and exploring mass spectrometry data from complexome profiling studies. Compatibility and reusability of the data is ensured by a standardized data and reporting format containing the "minimum information required for a complexome profiling experiment" (MIACE). The data can be accessed through a user-friendly web interface, as well as programmatically using the REST API portal. Additionally, all complexome profiles available on CEDAR can be inspected directly on the website with the profile viewer tool that allows the detection of correlated profiles and inference of potential complexes. In conclusion, CEDAR is a unique, growing and invaluable resource for the study of protein complex composition and dynamics across biological systems.

bioinformatics↗

bioRxiv2020

A ferredoxin bridge connects the two arms of plant mitochondrial complex I

Mitochondrial complex I is the main site for electron transfer to the respiratory chain and generates much of the proton gradient across the inner mitochondrial membrane. It is composed of two arms, which form a conserved L-shape. We report the structures of the intact, 47-subunit mitochondrial complex I from Arabidopsis thaliana and from the green alga Polytomella sp. at 3.2 and 3.3 [A] resolution. In both, a heterotrimeric {gamma}-carbonic anhydrase domain is attached to the membrane arm on the matrix side. Two states are resolved in A. thaliana complex I, with different angles between the two arms and different conformations of the ND1 loop near the quinol binding site. The angle appears to depend on a bridge domain, which links the peripheral arm to the membrane arm and includes an unusual ferredoxin. We suggest that the bridge domain regulates complex I activity. One sentence summaryThe activity of complex I depends on the angel between its two arms, which, in plants, is adjusted by a protein bridge that includes an unusual ferredoxin. The authors responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) are: Hans-Peter Braun (braun@genetik.uni-hannover.de) and Werner Kuhlbrandt (werner.kuehlbrandt@biophys.mpg.de).

plant biology↗

bioRxiv2020

Protein Interaction Patterns in Arabidopsis thaliana Leaf Mitochondria Change in Response to Illumination

Mitochondrial biology is underpinned by the presence and activity of large protein complexes participating in the organelle-located parts of cellular respiration, the TCA cycle and oxidative phosphorylation. While the enzymatic roles of these complexes are undisputed, little is known about the interactions of the subunits beyond their presence in the monomeric protein complexes and their functions in regulating mitochondria metabolism. By applying one of the most important regulatory cues for plant metabolism, the presence or absence of light, we here assess the changes in the composition and molecular mass of known mitochondrial protein complexes by employing a differential complexome profiling strategy. Covering a mass range up to 25 MDa, we demonstrate dynamic associations of TCA-cycle enzymes and of OXPHOS components. The data presented here form the basis for future studies aiming to advance our understanding of the role of protein:protein interactions in the regulation of plant mitochondrial functions.

plant biology↗

bioRxiv2020

Estimating the number of protein molecules in a plant cell: a quantitative perspective on proteostasis and amino acid homeostasis during progressive drought stress

During dehydration cellular proteostasis as well as amino acid homeostasis are severely challenged, since the decrease in photosynthesis induces massive proteolysis. Thus, we selected progressive drought stress in Arabidopsis thaliana as a model to investigate the balance between protein and free amino acid homeostasis on a quantitative level. We analyze the mass protein composition of rosette leaves and estimate, how many protein molecules are present in a plant cell and its subcellular compartments. Under control conditions, an average Arabidopsis mesophyll cell contains about 25 billion protein molecules and 80% of them are localized in the chloroplasts. Severe water deficiency leads to degradation of more than 40% of the leaf proteome and thus causes a drastic shift towards the free amino acid pool. Stress induced proteolysis of half of the 400 million RubisCO hexadecamers present in the chloroplasts of an individual mesophyll cell alone doubles the cellular content in free amino acids. A major fraction of the amino acids released from proteins is channeled into the synthesis of proline as a compatible osmolyte. Complete oxidation of the remaining part as an alternative respiratory substrate can fully compensate the lack of carbohydrates derived from photosynthesis for several hours.

plant biology↗