Nature cell biology

Cell cycle-specific phase separation regulated by protein charge blockiness

Sidharth Sirdeshmukh

Research Associate, Dewpoint

The general idea is that the patterns of charge differences in proteins will influence the kinetics of their phase separation-guided reassembly. Charge blocks are stretches of amino acids with similar charge, and ‘blockiness’ is the alternation of blocks of opposite charge (+/-). If we make these blocks shorter, then droplet formation is impeded, and droplets that previously existed dissolve/ diffuse. Hyperphosphorylation during mitosis, lengthens the blocks, which encourages droplet formation. Tuning the lengths, the total number, sequence, and likely stochasticity of these kinds of blocks will likely result in favorable LLPS dynamics/ arrangements for diseases with known condensate MOA.

Nature cell biology

NANOG prion-like assembly mediates DNA bridging to facilitate chromatin reorganization and activation of pluripotency

Sidharth Sirdeshmukh

Research Associate, Dewpoint

NANOG is a transcription factor that can reestablish ground-state pluripotency in stem cells. The authors of this paper sought to investigate the LLPS dynamics that resulted from amino acid-level differences in NANOG c-termini, that may drive this effect. Changing all tryptophans to alanines (WT to W8A) resulted in smaller monomeric assemblies of NANOG, which was not favorable for droplet formation. Additionally, FRAP experiments confirmed that these larger WT assemblies recover from photobleaching more slowly than W8A. CHIP-seq experiments show that these amino acid changes influence the regions of chromatin DNA recognized by WT and W8A, which connects these findings to the actual biology of pluripotency control. From this paper it is worth considering whether a similar strategy of systematically substituting amino acids in c-termini of other core transcription factors (ie. OCT4, SOX2), or other proteins with amyloid-like behaviors, would deliver favorable LLPS events, and subsequently unlock the doors to multi-factor ESC fate control.