Biology subjects

Bölker, M.

Publications and source records attributed to Bölker, M..

3 recordsLinked to original sources

bioRxiv2022

Selective accumulation of matrix proteins inside of peroxisomal subdomains

Formation of specialized reaction spaces prevents interference between distinct cellular pathways. Peroxisomes are cellular compartments involved in a large diversity of metabolic processes. How peroxisomes differentiate into subpopulations and by which mechanism intraorganellar domains are formed remains largely elusive. Here, we report on enzymes from the fungus Ustilago maydis, which accumulate inside of peroxisomal subdomains. We describe a short peptide motif (Thr-Ile-Ile-Val) sufficient to trigger focal localization. Mining for proteins with similar motifs uncovered several peroxisomal matrix proteins that accumulate in intraorganellar foci. These foci are enriched in the enzyme urate oxidase - a typical constituent of the paracrystalline core of peroxisomes. Upon peroxisome proliferation uneven distribution of focal structures results in the formation of peroxisome subpopulations with different protein content. The underlying principle of subdomain formation is evolutionary conserved in mammalian peroxisomes and formation of similar foci was also observed inside of mitochondria. We propose that peroxisomal proteins show an individual propensity to self-assemble. This formation of protein aggregates appears to be a ubiquitous driving force to spatially organize the peroxisomal proteome.

cell biology↗

bioRxiv2022

Dually targeted proteins regulate proximity between peroxisomes and partner organelles

Peroxisomes play a central role in fatty acid metabolism. To correctly target to peroxisomes, proteins require specialized targeting signals. One mystery in the field is sorting of proteins that carry both a targeting signal for peroxisomes as well as for other organelles such as mitochondria or the endoplasmic reticulum (ER). Exploring several of these dually localized proteins in Saccharomyces cerevisiae, we observed that they can act as dynamic tethers bridging organelles together through an affinity for organelle-destined targeting factors. We show that this mode of tethering involves the peroxisome import machinery, the ER- mitochondria encounter structure (ERMES) in the case of mitochondria and the GET complex in the case of the ER. Depletion of each of the targeting factors resulted in the accumulation of smaller peroxisomes. We propose that dual targeting of proteins occurs at contact sites and that protein import per se contributes to the maintenance of these membrane proximities. This introduces a previously unexplored concept of how targeting of dual affinity proteins can support organelle attachment, growth and communication.

cell biology↗

bioRxiv2019

An Unconventional Melanin Biosynthetic Pathway in Ustilago maydis

Ustilago maydis is a phytopathogenic fungus responsible for corn smut disease. Although it is a very well established model organism for the study of plant-microbe interactions, its biosynthetic potential has not been totally explored. By analyzing U. maydis genome, we identified a biosynthetic gene cluster whose activation led to the production of a black melanin pigment. Single deletion mutants of the cluster genes revealed that five encoded enzymes are required for the accumulation of the black pigment, including three polyketide synthases (pks3, pks4 and pks5), a cytochrome P450 monooxygenase (cyp4) and a protein with similarity to versicolorin B-synthase (vbs1). Moreover, metabolic profiles of the mutants defective for pks3 and pks4 indicated that the products of these genes catalyze together the first step in the melanin biosynthetic pathway since none of the mutants accumulated any melanin or intermediate products. Mutants deleted for pks5 produced orsellinic acid (OA) and triacetic acid lactone (TAL), suggesting that both products are produced by Pks3 and Pks4. It might thus demonstrate that Pks5 plays a role in a reaction downstream of that catalyzed by Pks3 and Pks4. OA and TAL were also found in extracts of a cyp4 deletion mutant along with several heterodimers of TAL and Pks5-derived orsellinic aldehyde compounds. According to their phenotypes and the intermediate products isolated from these strains, Cyp4 and Vbs1 seem to be involved in reactions downstream of Pks5. Our findings suggest that U. maydis synthesizes a new melanin based on coumarin and pyran-2-one intermediates, while most fungal melanins are derived from 1,8-dihydroxynaphthalene (DHN) or L-3,4-dihydroxyphenylalanine (L-DOPA). Along with these observations, this work also provides an insight into the mechanisms of polyketide synthases in this filamentous fungus. IMPORTANCEUstilago maydis represents one of the major threats for maize plants since it is responsible for corn smut disease, which generates considerable economical losses around the world. Therefore, contributing to a better understanding of the biochemistry of defense mechanisms used by U. maydis to protect itself against harsh environments, as the synthesis of melanin, could provide improved biological tools for tackling the problem and protect the crops. In addition, the fact that this fungus synthesizes melanin in a very unique way, requiring more than one polyketide synthase for producing this secondary metabolite, gives a different perspective on the complexity of these multimodular enzymes and their evolution in the fungal kingdom.

genetics↗