Graduate Students Mini-Symposium IV 2025

13:15 h Nidhi Kalidas - AG Thanbichler

Analysis of the interplay between chromosome segregation and cell division in Caulobacter crescentus.

In the model bacterium Caulobacter crescentus, the spatiotemporal regulation of cell division is mediated by the P-loop ATPase MipZ. MipZ inhibits FtsZ polymerization and forms a bipolar protein gradient that prevents the assembly of the cytokinetic Z-ring close to the cell poles, thereby limiting cytokinesis to the cell center. The subcellular distribution of MipZ is determined by various interaction partners, one of which is the essential chromosome segregation protein ParB. Previous work has shown that ParB interacts with MipZ monomers and recruits them to the pole, stimulating their dimerization. The release of MipZ dimers from ParB, their non-specific interaction with pole-proximal chromosomal DNA and their sub­sequent dissociation upon spontaneous ATP hydrolysis give rise to a dynamic gradient of MipZ dimers on the nucleoid, with concentration maxima at the cell poles and a minimum at mid-cell. The role of ParB in MipZ gradient formation is intriguing. However, mechanistic insights into the ParB-assisted dimerization of MipZ are still missing. In this study, we mapped the sites of ParB that mediate its interaction with MipZ. Our results identify the C-terminal region of ParB as the main interaction interface. These findings explain how ParB achieves its dual function in chromosome segregation and division site placement and lay the foundation to further investigate the molecular mechanism underlying ParB-dependent MipZ dimerization, thereby providing critical new insights into chromosome segregation and cell division in C. crescentus.

13:45 h Ana Lago Maciel - ENG Rebelein

Methylthio-alkane reductases use nitrogenase metalloclusters for carbon-sulfur bond cleavage

Methylthio-alkane reductases convert methylated sulfur compounds to methanethiol and small hydrocarbons, a process with important environmental and biotechnological implications. These enzymes are classified as nitrogenase-like enzymes, despite lacking the ability to convert dinitrogen to ammonia, raising fundamental questions about the factors controlling their activity and specificity. Here, we present the first molecular structure of the methylthio-alkane reductase, which reveals large metalloclusters, including the P-cluster and the [Fe₈S₉C]-cluster, previously only found in nitrogenases. Our findings suggest that distinct metallocluster coordination, surroundings, and substrate channels, determine the activity of these related metalloenzymes. This study provides new insights into nitrogen fixation, sulfur-compound reduction, and hydrocarbon production. We also shed light on the evolutionary history of P-cluster and [Fe₈S₉C]-cluster-containing reductases emerging prior to nitrogenases.