Biology subjects

Coronas-Serna, J. M.

Publications and source records attributed to Coronas-Serna, J. M..

2 recordsLinked to original sources

bioRxiv2026

PAK-family kinases promote cell fusion irreversibility by preventing cell wall repair

Cell-cell fusion is critical for the sexual life cycle, as it drives the unidirectional transition between haploid and diploid phases. In fungi, fusion requires not only plasma membrane merging but also local cell wall removal. However, the integrity of the cell wall, which resists internal turgor pressure and is essential for survival, is normally monitored by a cell wall integrity pathway (CIP) involving Rho1 GTPase, protein kinase C (PKC) and MAPK signaling, which promotes damage repair. How the CIP allows localized cell wall degradation is not known. In the fission yeast Schizosaccharomyces pombe, we previously identified pak2{Delta} mutants that exhibit transient fusion: cells briefly fuse and exchange cytoplasmic contents, which signal catastrophic haploid meiosis, but then reseal their fusion pore. Here, we show that PAK-family kinase activity is essential for cell-cell fusion, with major and minor contribution for Pak2 and the essential Pak1, respectively. Strikingly, osmotic stabilization largely suppresses all PAK-associated fusion defects, pointing to a role in cell-wall remodeling. Pak2 accumulates at the fusion site, where it promotes fusion pore opening and expansion. In its absence, Rho1-GTP, PKC and beta-glucan synthase Bgs4 show elevated levels at the fusion site, and their partial loss-of-function rescues fusion. Pak1 mutants have elevated MAPK activity. Thus, Pak2 and Pak1 both antagonize the CIP. Furthermore, correlative light and cryo-soft-X-ray tomography reveals that resealed pores in PAK mutants rebuilt an intact cell wall. We conclude that PAKs enforce fusion directionality by antagonizing cell-wall repair mechanisms that otherwise restore separation between mating partners.

cell biology↗

bioRxiv2019

The TIR-domain containing effectors BtpA and BtpB from Brucella abortus block energy metabolism

Brucella species are facultative intracellular Gram-negative bacteria relevant to animal and human health. Their ability to establish an intracellular niche and subvert host cell pathways to their advantage depends on the delivery of bacterial effector proteins through a type IV secretion system. Brucella Toll/Interleukin-1 Receptor (TIR)-domain-containing proteins BtpA (also known as TcpB) and BtpB are among such effectors. Although divergent in primary sequence, they interfere with Toll-like receptor (TLR) signaling to inhibit the innate immune responses. However, the molecular mechanisms implicated still remain unclear. To gain insight into the functions of BtpA and BtpB, we expressed them in the budding yeast Saccharomyces cerevisiae as a eukaryotic cell model. We found that both effectors were cytotoxic and that their respective TIR domains were necessary and sufficient for yeast growth inhibition. Growth arrest was concomitant with actin depolymerization, endocytic block and a general decrease in kinase activity in the cell, suggesting a failure in energetic metabolism. Indeed, levels of ATP and NAD+ were low in yeast cells expressing BtpA and BtpB TIR domains, consistent with the recently described enzymatic activity of some TIR domains as NAD+ hydrolases. In human epithelial cells, both BtpA and BtpB expression reduced intracellular total NAD levels. In infected cells, both BtpA and BtpB contributed to reduction of total NAD, indicating that their NAD+ hydrolase functions are active intracellularly during infection. Overall, combining the yeast model together with mammalian cells and infection studies our results show that BtpA and BtpB modulate energy metabolism in host cells through NAD+ hydrolysis, assigning a novel role for these TIR domain-containing effectors in Brucella pathogenesis.

microbiology↗