bims-nucpor 2023-03-26 papers

Issue of 2023–03–26
three papers selected by
Sara Mingu, Johannes Gutenberg University

Proc Natl Acad Sci U S A. 2023 Mar 28. 120(13): e2202815120

The capsid lattice engages a bipartite NUP153 motif to mediate nuclear entry of HIV-1 cores.

Increasing evidence has suggested that the HIV-1 capsid enters the nucleus in a largely assembled, intact form. However, not much is known about how the cone-shaped capsid interacts with the nucleoporins (NUPs) in the nuclear pore for crossing the nuclear pore complex. Here, we elucidate how NUP153 binds HIV-1 capsid by engaging the assembled capsid protein (CA) lattice. A bipartite motif containing both canonical and noncanonical interaction modules was identified at the C-terminal tail region of NUP153. The canonical cargo-targeting phenylalanine-glycine (FG) motif engaged the CA hexamer. By contrast, a previously unidentified triple-arginine (RRR) motif in NUP153 targeted HIV-1 capsid at the CA tri-hexamer interface in the capsid. HIV-1 infection studies indicated that both FG- and RRR-motifs were important for the nuclear import of HIV-1 cores. Moreover, the presence of NUP153 stabilized tubular CA assemblies in vitro. Our results provide molecular-level mechanistic evidence that NUP153 contributes to the entry of the intact capsid into the nucleus.

Keywords: HIV-1 capsid; NUP153; RRR-motif; lattice stabilization; nuclear entry

DOI: https://doi.org/10.1073/pnas.2202815120

J Mol Biol. 2023 Mar 16. pii: S0022-2836(23)00107-9. [Epub ahead of print] 168051

Cryo-electron microscopy reveals the structure of the nuclear pore complex.

Linhua Tai, Guoliang Yin, Fei Sun, Yun Zhu.

The nuclear pore complex (NPC) is a giant protein assembly that penetrates the double layers of the nuclear membrane. The overall structure of the NPC has approximately eightfold symmetry and is formed by approximately 30 nucleoporins. The great size and complexity of the NPC have hindered the study of its structure for many years until recent breakthroughs were achieved by integrating the latest high-resolution cryo-electron microscopy (cryo-EM), the emerging artificial intelligence-based modeling and all other available structural information from crystallography and mass spectrometry. Here, we review our latest knowledge of the NPC architecture and the history of its structural study from in vitro to in situ with progressively improved resolutions by cryo-EM, with a particular focus on the latest subnanometer-resolution structural studies. The future directions for structural studies of NPCs are also discussed.

DOI: https://doi.org/10.1016/j.jmb.2023.168051

Proc Natl Acad Sci U S A. 2023 Mar 28. 120(13): e2221432120

Mechanomemory in protein diffusivity of chromatin and nucleoplasm after force cessation.

Fazlur Rashid, Wenjie Liu, Qianchun Wang, Baohua Ji, Joseph Irudayaraj, Ning Wang.

It is known that external mechanical forces can regulate structures and functions of living cells and tissues in physiology and diseases. However, after cessation of the force, how structures are altered in response to the dynamics of the chromatin and molecules in the nucleoplasm remains elusive. Here, using single-molecule imaging approaches, we show that exogenous local forces via integrins applied for 2 to 10 min decondensed the chromatin and increased chromatin and nucleoplasm protein mobility inside the nucleus, leading to elevated diffusivity of single protein molecules in the nucleoplasm, tens of minutes after the cessation of force. Diffusion experiments with fluorescence correlation spectroscopy in live single cells show that the mechanomemory in chromatin and nucleoplasm protein diffusivity was regulated by nuclear pore complexes. Protein molecular dynamics simulation recapitulated the experimental findings in live cells and showed that nucleoplasm protein diffusivity was regulated by the number of nuclear pore complexes. The mechanomemory in elevated protein diffusivity of the nucleoplasm after force cessation represents a physical process that reverses protein-protein condensation in phase separation via unjamming of the chromatin. Our findings of mechanomemory in chromatin and nucleoplasm protein diffusivity suggest that the effect of force on the nucleus remains tens of minutes after force cessation and thus is more far-reaching than previously anticipated.

Keywords: diffusion; force; nucleus

DOI: https://doi.org/10.1073/pnas.2221432120