Breaking New Cell Biology Research

Dr. Brian Chait, the Camille and Henry Dreyfus Professor, at Rockefeller University, will be visiting Yale to give a talk entitled “On Methods for Probing the Protein Interactions” on May 9, 2023. His lab focuses on developing tools, centering around mass spectrometry approaches to study the structure and function of biomolecular assemblies. Caroline Brown had the pleasure of chatting with him prior to his visit to Yale to find out about his personal and scientific journey.

A recently published Yale study explored how cancer cell plasticity — which refers to the ability of cells to adapt their phenotypes in response to environmental signals without undergoing genetic alterations — might impact the development, progression and treatment of cancer.

Super-resolution microscopy can reveal small subcellular structures invisible to classical light microscopes thanks to its tenfold improved resolution (20-70 nm). The broad application of the new technology has however been hampered by the low throughput of these new technologies: in a typical workday, a researcher can image only about 10 mammalian cells. The Bewersdorf and Baddeley labs have now published a next-generation super-resolution microscope which can image 1,000 to 10,000 cells in an automated manner in 24 hours. This enables future, previously inaccessible studies that require the comparison of many experimental conditions or have high demands for sample size.

Entering nucleus is a complicated process critical to the infectivity of HIV. Shen et al. built DNA-origami-based nuclear pore complex mimics to elucidate important capsid-nucleoporin interactions that underlie the nuclear entry of HIV-1 core.

Tail-anchored (TA) proteins contain a single C-terminal transmembrane domain (TMD) that is captured by the cytosolic Get3 in yeast (TRC40 in humans). Get3 delivers TA proteins to the Get1/2 complex for insertion into the endoplasmic reticulum (ER) membrane. How Get1/2 mediates insertion of TMDs of TA proteins into the membrane is poorly understood. Using bulk fluorescence and microfluidics assays, we show that Get1/2 forms an aqueous channel in reconstituted bilayers. We estimate the channel diameter to be ∼2.5 nm wide, corresponding to the circumference of two Get1/2 complexes. We find that the Get3 binding can seal the Get1/2 channel, which dynamically opens and closes. Our mutation analysis further shows that the Get1/2 channel activity is required to release TA proteins from Get3 for insertion into the membrane. Hence, we propose that the Get1/2 channel functions as an insertase for insertion of TMDs and as a translocase for translocation of C-terminal hydrophilic segments.

Sun et al. show that proteins with marginally hydrophobic signal sequences pause at the Sec61 translocon channel on their way into the ER and require Sec63/BiP to overcome the pause and facilitate subsequent protein folding in the ER. This pause-and-go mechanism prevents protein aggregation inside the ER during chaperone deficiency.

To aid their growth, young proteins enlist the protection of a chaperone called BiP (binding immunoglobulin protein), but how our cells make this match has remained unclear. Scientists at the Yale Nanobiology Institute have now decoded the protein signal sequences that determine the movement and timing of the protein-chaperone match – effectively revealing the blueprint for how our proteins reach maturity.

The trans-Golgi Network (TGN) sorts newly synthesized proteins to their destination via vesicular transport carriers. Despite the functional significance of packaging processes at the TGN, the sorting of soluble proteins remains enigmatic. The Golgi resident protein Cab45 is a significant regulator of secretory cargo sorting at the TGN. Cab45 oligomerizes upon transient Ca2+ influx, recruits soluble cargo molecules (clients), and packs them into vesicles. However, the identity of client molecules packed into Cab45 vesicles is scarce. Therefore, we used a highly efficient secretome analysis technology called hiSPECs. Intriguingly, we observed that Cab45 deficient cells manifest hypersecretion of lysosomal hydrolases. Specifically, Cab45 deficient cells secrete the precursors of prosaposin and progranulin. In addition, lysosomes in these cells show an aberrant perinuclear accumulation suggesting a new role of Cab45 in lysosomal positioning.

Synthetic DNA clamps close their jaws to draw tubes from liposomes, resembling the work of membrane-deforming proteins.