Subcellular protein localization in B. subtilis

Division Of Basic Sciences - Nci

Investigators

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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. Our lab has extended our analysis on the assembly of the bacterial spore coat and cortex as a model for understanding cellular morphogenesis. A nearly 50-year old observation indicated that assembly of the spore cortex (a peptidoglycan shell that covers the forespore) requires assembly of an outer, proteinaceous, shell termed the spore "coat", even though two structures are separated by a membrane. This year, we reported that a single protein links the morphogenesis of both spatially separated structures. A genetic approach identified the protein "SpoVID" as a central regulator in this developmental checkpoint. Specifically, we found that SpoVID harbors a functional "LysM" domain which is usually implicated in binding mature peptidoglycan. We showed that this domain in SpoVID instead interacts with peptidoglycan precursors. We also showed that this domain is occluded when the major morphogenetic protein that comprises the spore coat is polymerized. We proposed a model in which proper assembly of the coat permits cortex assembly, due to the occluded LysM domain of SpoVID. However, upon improper coat assembly, the LysM domain of SpoVID is liberated, whereupon it sequesters peptidoglycan precursors to prevent cortex assembly. Thus, SpoVID represents a developmental checkpoint that directly monitors the assembly of a physical structure to permit continuation through a differentiation program. A manuscript describing these results were published in Developmental Cell in 2022. Previously, we have used our basic science discoveries to develop artificial bacterial spore-like particles 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 has been posted to bioRxiv and is currently under peer review after revisions. 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. We are currently testing peptide antigens from various bacterial pathogens, including Staphylococcus aureus.