Ludtke, S. | Search bioRxiv

bioRxiv2021

Cryo-ET distinguishes platelets during pre-acute myeloid leukemia from steady state hematopoiesis

Early diagnosis of acute myeloid leukemia (AML) in the pre-leukemic stage remains a clinical challenge, as pre-leukemic patients show no symptoms, lacking any known morphological or numerical abnormalities in blood cells. Here, we demonstrate that platelets with structurally abnormal mitochondria emerge at the pre-leukemic phase of AML, preceding detectable changes in blood cell counts or detection of leukemic blasts in blood. We visualized frozen-hydrated platelets from mice at different time points during AML development in situ using electron cryo-tomography (cryo-ET) and identified intracellular organelles through an unbiased semi-automatic process followed by quantitative measurement. A large proportion of platelets exhibited changes in the overall shape and depletion of organelles in AML. Notably, 23% of platelets in pre-leukemic cells exhibit abnormal, round mitochondria with unfolded cristae, accompanied by a significant drop in ATP levels and altered expression of metabolism-related gene signatures. Our study demonstrates that detectable structural changes in pre-leukemic platelets may serve as a biomarker for the early diagnosis of AML.

biophysics↗

bioRxiv2020

In situ structure of the AcrAB-TolC efflux pump at subnanometer resolution

In Gram-negative bacteria, tripartite efflux pump AcrAB-TolC plays a prominent role in antibiotic resistance. We have used high resolution cryo-ET to visualize the structure of Escherichia coli AcrAB-TolC at a 7 [A] resolution in intact cells. The resulting structures show the detailed architecture of the assembled complex embedded into cell envelope. Interactions with the inner membrane enable crosstalk between AcrB and TolC through AcrA, suggesting that assembly in the native cellular environment is critical for the pump activation mechanism, where the allosteric activating signal is triggered by the alternate binding of AcrA to the lipid membrane and AcrB porter domain. We establish a platform for high resolution in situ structural studies of bacteria efflux pump, which can yield critical information in understanding complex assemblies function. One sentence summaryA 7 [A] in situ structure of the AcrAB-TolC pump from bacteria by cryo-ET reveals mechanisms for active efflux.

biophysics↗