Biology subjects

Izquierdo-Martinez, A.

Publications and source records attributed to Izquierdo-Martinez, A..

3 recordsLinked to original sources

bioRxiv2026

Nucleoid-binding protein RicO anchors replication origins to the membrane to ensure correct chromosome segregation in Staphylococcus aureus

The mechanisms underlying chromosome segregation in bacteria, particularly in non-canonical models, remain incompletely understood. The coccoid bacterium Staphylococcus aureus encodes a limited set of conserved proteins involved in chromosome segregation, including the Structural Maintenance of Chromosomes (SMC) complex and an incomplete partition system. Here, we identified a protein of previously unknown function that interacts with the nucleoid and ensures accurate chromosome segregation in S. aureus. RicO (Regulator and Insulator of Chromosomal Origins) contains a conserved N-terminal DNA-binding domain that recognizes a specific sequence motif in the origin-proximal region of the chromosome, as well as a C-terminal amphipathic helix that interacts with the cell membrane, thereby bridging DNA and the membrane. RicO localizes in membrane-proximal foci at the tip of each hemisphere (or cell poles). Cells lacking RicO fail to correctly position replication origins at the cell poles and have weakened genomic interactions in the origin-proximal region, resulting in chromosome segregation defects. The combined absence of RicO and a functional SMC complex leads to nearly half of the population appearing as anucleate cells, indicating that these two systems are key contributors to chromosome segregation in S. aureus. Collectively, our data support a model in which RicO anchors chromosomal origins at the cell periphery to ensure genome maintenance in this spherical bacterial pathogen.

microbiology↗

bioRxiv2025

Chromosome segregation dynamics during the cell cycle of Staphylococcus aureus

Research on chromosome organization and cell cycle progression in spherical bacteria, particularly Staphylococcus aureus, remains limited and fragmented. In this study, we established a working model to investigate chromosome dynamics in S. aureus using a Fluorescent Repressor-Operator System (FROS), which enabled precise localization of specific chromosomal loci. This approach revealed that the S. aureus cell cycle and chromosome replication cycle are not coupled, with cells exhibiting two segregated origins of replication at the start of the cell cycle. The chromosome has a specific origin-terminus-origin conformation, with origins localizing near the membrane, towards the tip of each hemisphere, or the "cell poles". We further used this system to assess the role of various proteins with a role in S. aureus chromosome biology, focusing on the ParB-parS and SMC-ScpAB systems. Our results demonstrate that ParB binds five parS chromosomal sequences and the resulting complexes influence chromosome conformation, but play a minor role in chromosome compaction and segregation. In contrast, the SMC-ScpAB complex plays a key role in S. aureus chromosome biology, contributing to chromosome compaction, segregation and spatial organization. Additionally, we systematically assessed and compared the impact of proteins linking chromosome segregation to cell division--Noc, FtsK, SpoIIIE and XerC--on origin and terminus number and positioning. This work provides a comprehensive study of the factors governing chromosome dynamics and organization in S. aureus, contributing to our knowledge on chromosome biology of spherical bacteria.

microbiology↗

bioRxiv2022

DipM controls multiple autolysins and mediates two regulatory feedback loops promoting cell constriction in C. crescentus

Proteins containing a catalytically inactive LytM-type endopeptidase domain have emerged as important regulators of cell wall-degrading enzymes in bacteria. Although these so-called LytM factors are wide-spread among species, the range of functions they fulfill and their precise modes of action are still incompletely understood. In this work, we study the LytM factor DipM, a protein required for proper cell division in the model species C. crescentus. We show that the LytM domain of DipM interacts directly with multiple autolysins, including the lytic transglycosylases SdpA and SdpB, the amidase AmiC and the putative carboxypeptidase CrbA, and stimulates the activities of SdpA and AmiC. The crystal structure of the LytM domain of DipM reveals conserved features, including a distinctive groove. Modeling studies suggest that this groove could represent the docking site of AmiC. The architecture of the binding interface in the DipM-AmiC complex is very similar to that observed for the LytM domain of EnvC in complex with its autoinhibitory restraining arm, suggesting a conserved role of the groove in the interaction of LytM factors with their (auto-)regulatory targets. In line with this hypothesis, a mutation in the groove abolishes DipM function. Interestingly, single-molecule tracking studies reveal that the recruitment of DipM and its regulatory targets SdpA and SdpB to the division site is mutually interdependent, with DipM establishing a self-reinforcing cycle that gradually increases lytic transglycosylase activity at the cell center as division progresses. At the same time, the DipM-dependent activation of AmiC leads to the production of denuded peptidoglycan, generating a spatial cue that attracts FtsN to the division site and thus, in turn, again promotes the recruitment of DipM. Collectively, these findings show that DipM is a central regulator that acts at the intersection of different peptidoglycan remodeling pathways and coordinates the activities of various classes of autolysins to promote cell constriction and daughter cell separation.

microbiology↗