Biology subjects

Ban, I.

Publications and source records attributed to Ban, I..

3 recordsLinked to original sources

bioRxiv2023

Universal features of Nsp1-mediated translational shutdown by coronaviruses

Nonstructural protein 1 (Nsp1) produced by coronaviruses shuts down host protein synthesis in infected cells. The C-terminal domain of SARS-CoV-2 Nsp1 was shown to bind to the small ribosomal subunit to inhibit translation, but it is not clear whether this mechanism is broadly used by coronaviruses, whether the N-terminal domain of Nsp1 binds the ribosome, or how Nsp1 specifically permits translation of viral mRNAs. Here, we investigated Nsp1 from three representative Betacoronaviruses - SARS-CoV-2, MERS-CoV, and Bat-Hp-CoV - using structural, biophysical, and biochemical assays. We revealed a conserved mechanism of host translational shutdown across the three coronaviruses. We further demonstrated that the N-terminal domain of Bat-Hp-CoV Nsp1 binds to the decoding center of the 40S subunit, where it would prevent mRNA and eIF1A binding. Structure-based biochemical experiments identified a conserved role of these inhibitory interactions in all three coronaviruses and showed that the same regions of Nsp1 are responsible for the preferential translation of viral mRNAs. Our results provide a mechanistic framework to understand how Betacoronaviruses overcome translational inhibition to produce viral proteins.

biochemistry↗

bioRxiv2022

Proliferative advantage of specific aneuploid cells drives evolution of tumor karyotypes

Most tumors have abnormal karyotypes, which arise from mistakes during mitotic division of healthy euploid cells and evolve through numerous complex mechanisms. In a recent mouse model with high levels of chromosome missegregation, chromosome gains dominate over losses both in pretumor and tumor tissues, whereas tumors are characterized by gains of chromosomes 14 and 15. However, the mechanisms driving clonal selection leading to tumor karyotype evolution remain unclear. Here we show, by introducing a mathematical model based on a concept of a macro-karyotype, that tumor karyotypes can be explained by proliferation-driven evolution of aneuploid cells. In pretumor cells, increased apoptosis and slower proliferation of cells with monosomies lead to predominant chromosome gains over losses. Tumor karyotypes with gain of one chromosome can be explained by karyotype-dependent proliferation, while for those with two chromosomes an interplay with karyotype-dependent apoptosis is an additional possible pathway. Thus, evolution of tumor-specific karyotypes requires proliferative advantage of specific aneuploid karyotypes. SignificanceMost tumors have an erroneous number of chromosomes, which arise from mistakes during division of healthy cells and evolve through numerous complex mechanisms, including chromosome missegregation, cell proliferation and cell death. However, understanding the mechanisms leading to tumor evolution from healthy cells is a hot topic. Here we show, by introducing a "macro-karyotype model", that perturbed number of chromosomes in tumor cells arises predominantly from faster division of cells characterized by a specific combination of chromosomes, or together with irregular cell death. This finding, strengthened by comparison of our theory with experimentally observed combination of chromosomes in different stages of tumor development, gives a direction for future experiments in identifying the key processes underlying tumor development.

biophysics↗

bioRxiv2018

Pivoting of microtubules driven by minus end directed motors leads to their alignment to form an interpolar bundle

At the beginning of mitosis, the cell forms a spindle made of microtubules and associated proteins to segregate chromosomes. An important part of spindle architecture is a set of antiparallel microtubule bundles connecting the two spindle poles. A key question is how microtubules extending at arbitrary angles form an antiparallel interpolar bundle. Here we show that microtubules meet at an oblique angle and subsequently rotate into antiparallel alignment. By combining experiments with theory, we show that microtubules from each pole search for those from the opposite pole by performing random angular movement. Upon contact of two microtubules, they slide sideways along each other towards the minus end, which we interpret as the action of minus end directed Cut7/kinesin-5 motors. In conclusion, random rotational motion helps microtubules from the opposite poles to find each other and subsequent accumulation of motors allows them to generate forces that drive interpolar bundle formation.

cell biology↗