Biology subjects

Hall, A. M. J.

Publications and source records attributed to Hall, A. M. J..

3 recordsLinked to original sources

bioRxiv2026

Lipid Changes due to Low O-GlcNAc and the Downstream Consequences

O-GlcNAc transferase (OGT) is an essential mammalian glycosyltransferase that installs O-GlcNAc onto thousands of cytosolic and nuclear proteins. Dysregulated glycosylation by OGT is associated with disease states, including cancer and neurodegeneration. However, cellular consequences of acute loss of O-GlcNAc remain poorly understood. Here, we employed a cell-permeable small molecule inhibitor of OGT, OSMI-4, coupled with transcriptomic and lipidomic analyses to characterize the effects of O-GlcNAc depletion in human cell lines. Loss of O-GlcNAc led to changes in expression of lipid metabolism genes and remodeling of the lipidome, with unsaturated phosphatidylcholines (PCs), saturated lysophosphatidylcholines (LPCs) and unsaturated storage lipids accumulating. We also observed increased lipid droplets. Our results suggest that polyunsaturated fatty acids (PUFAs) accumulate in the membrane under low O-GlcNAc conditions and that cells buffer this accumulation by removing PUFAs from membrane lipids and sequestering them in lipid droplets. We found that treatment with OSMI-4 sensitizes cells to ferroptosis inducers, likely because accumulated cell membrane PUFAs undergo peroxidation. Taken together, our results highlight lipid remodeling as an important process that mediates the downstream effects of loss of O-GlcNAc. It may be possible to exploit the synergy between OGT inhibitors and ferroptosis inducers for therapeutic benefit.

cell biology↗

bioRxiv2021

A tRNA-acetylating toxin and detoxifying enzyme in Mycobacterium tuberculosis.

Toxin-antitoxin (TA) systems allow bacteria to adapt to changing environments without altering gene expression. Despite being overrepresented in Mycobacterium tuberculosis (Mtb), their individual physiological roles remain elusive. We describe a TA system in Mtb which we have named TacAT due to its homology to previously discovered systems in Salmonella. The toxin, TacT, blocks growth by acetylating glycyl-tRNAs and inhibiting translation. Its effects are reversed by the enzyme peptidyl tRNA hydrolase (Pth), which also cleaves peptidyl tRNAs that are prematurely released from stalled ribosomes. Pth is essential in most bacteria and thereby has been proposed as a promising drug target for complex pathogens like Mtb. Transposon sequencing data suggest that the tacAT operon is nonessential for Mtb growth in vitro, and premature stop mutations in this TA system present in some clinical isolates suggest that it is also dispensable in vivo. We assessed whether TacT modulates pth essentiality in Mtb, as drugs targeting Pth might be ineffective if TacAT is disrupted. We find that pth essentiality is unaffected by the absence of tacAT. These results highlight a fundamental aspect of mycobacterial biology and indicate that Pths essential role hinges on its peptidyl-tRNA hydrolase activity. Our work underscores Pths potential as a viable target for new antibiotics.

microbiology↗

bioRxiv2018

In depth biochemical and structural analysis of a Gram-positive type IV pilus

Type IV pili (Tfp) are functionally versatile filaments, widespread in prokaryotes, that belong to a large class of filamentous nanomachines known as type IV filaments (Tff). Although Tfp have been extensively studied in several Gram-negative pathogens where they function as key virulence factors, many aspects of their biology remain poorly understood. Here, we performed a global biochemical and structural analysis of Tfp in a recently emerged Gram-positive model, Streptococcus sanguinis. In particular, we focused on the five pilins and pilin-like proteins involved in Tfp biology in S. sanguinis. We found that the two major pilins, PilE1 and PilE2, (i) follow widely conserved principles for processing by the prepilin peptidase PilD and for assembly into filaments; (ii) display only one of the post-translational modifications frequently found in pilins, i.e. a methylated N-terminus; (iii) are found in the same hetero-polymeric filaments; and (iv) are not functionally equivalent. The 3D structure of PilE1, solved by NMR, revealed a classical pilin fold with a highly unusual flexible C-terminus. Intriguingly, PilE1 more closely resembles pseudopilins forming shorter Tff than bona fide Tfp-forming major pilins, underlining the evolutionary relatedness among different Tff. Finally, we show that S. sanguinis Tfp contain a low abundance of three additional proteins processed by PilD, the minor pilins PilA, PilB, and PilC. These findings provide the first global biochemical and structural picture of a Gram-positive Tfp and have fundamental implications for our understanding of a widespread class of filamentous nanomachines.

microbiology↗