Biophysical Characterization of Chlamydia trachomatis CT584 Supports Its Potential Role as a Type III Secretion Needle Tip Protein

This is the published version. Copyright American Chemical SocietyChlamydia are obligate intracellular bacterial pathogens that cause a variety of diseases. Likemany Gram-negative bacteria, they employ type III secretion systems (T3SS) for invasion, establishing and maintaining their unique intracellular niche, and possibly cellular exit. Computational structure prediction indicated that ORF CT584 is homologous to other T3SS needle tip proteins. Tip proteins have been shown to be localized to the extracellular end of the T3SS needle and play a key role in controlling secretion of effector proteins. We have previously demonstrated that T3SS needle tip proteins from different bacteria share many biophysical characteristics. To support the hypothesis that CT584 is a T3SS needle tip protein, biophysical properties of CT584 were explored as a function of pH and temperature, using spectroscopic techniques. Far-UV circular dichroism, Fourier transform infrared spectroscopy, UV absorbance spectroscopy, ANS extrinsic fluorescence, turbidity, right angle static light scattering, and analytical ultracentrifugation were all employed to monitor the secondary, tertiary, quaternary, and aggregation behavior of this protein. An empirical phase diagram approach is also employed to facilitate such comparisons. These analyses demonstrate that CT584 shares many biophysical characteristics with other T3SS needle tip proteins. These data support the hypothesis that CT584 is a member of the same functional family, although future biologic analyses are required

Oxaliplatin disrupts nucleolar function through biophysical disintegration

Platinum (Pt) compounds such as oxaliplatin are among the most commonly prescribed anti-cancer drugs. Despite their considerable clinical impact, the molecular basis of platinum cytotoxicity and cancer specificity remain unclear. Here we show that oxaliplatin, a backbone for the treatment of colorectal cancer, causes liquid-liquid demixing of nucleoli at clinically relevant concentrations. Our data suggest that this biophysical defect leads to cell-cycle arrest, shutdown of Pol I-mediated transcription, and ultimately cell death. We propose that instead of targeting a single molecule, oxaliplatin preferentially partitions into nucleoli, where it modifies nucleolar RNA and proteins. This mechanism provides a general approach for drugging the increasing number of cellular processes linked to biomolecular condensates