Subcellular protein localization in B. subtilis

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

In the last year, we have continued our studies that investigate how cells differentiate in an effort to understand how these processes may fail during diseases like cancer. In this report, we outline progress that we have made in the past year that extends our studies on how large subcellular structures assemble during growth and development of the model organism Bacillus subtilis and Staphylococcus aureus, and how synthetic bacterial spores ("SSHELs") may be used as a cell-specific drug delivery system. First, we discovered a previously uncharacterized cell division gene in Staphylococcus aureus, which is a leading cause of nosocomial infections in the U.S. This gene, which we named "pcdA", encodes for an ATPase that we showed directly recruits the cell division machinery to the correct cell division plane. Deletion of this gene resulted in a virulence defect in a mouse model and increased susceptibility to several antibiotics commonly used in the clinic, suggesting that targeting PcdA could provide a novel therapeutic strategy to combat Staphylococcal infections. Additionally, we investigated two regulatory mechanisms that promote progression through bacterial sporulation, a relatively simple developmental program. In the first project, we investigated how a transcription factor is specifically activated in only one differentiating daughter cell. Using super-resolution microscopy, our work indicated that an activating protein is asymmetrically positioned on one face of a polar division septum. We also isolated a mutation in a structural gene that disrupted this biased localization and demonstrated that the cell division machinery itself is involved in this asymmetric localization. In the second project, we discovered a previously unknown pathway that involves cell-cell signaling during spore formation to promote heterogeneity in a clonal population of cells. In this mechanism, cells that enter sporulation early signal back to late-entering cells and delay their entry into sporulation. Deletion of this pathway resulted in more homogeneous sporulation entry. Thus, when considering the generation of heterogeneity in a population, our results suggested that cell-cell signalling must also be considered. Finally, we previously, have used our basic science discoveries to develop artificial bacterial spore-like particles termed "SSHELs" that we proposed can be used as novel drug delivery vehicles. In the last year, we have engineered these particles to contain a sample drug cargo and have modified the surface of these particles to directly bind to certain epitopes that are overrepresented on cancer cells. We have demonstrated, in a mouse model, that these particles are safe when administered and can prevent the growth of tumors. Further, we demonstrated that drug delivery using this platform resulted in fewer side effects than a leading nanoparticle-mediated method. A manuscript describing these results was published in Cell Reports and was featured on the cover of the journal. Finally, we are investigating the efficacy of artificial spore-like particles as a vaccine display platform that displays peptide antigens. Although peptide antigens may provide high specificity and are relatively easy to generate, they are usually largely ineffective because of their short biological half-life.