Search bioRxiv⌕ Search

Biology subjects

Shima, M.

Publications and source records attributed to Shima, M..

3 recordsLinked to original sources

CGK733 binds to adenine nucleotide translocator 2 and modulates mitochondrial function and protein translation

Chemical genetics is a powerful strategy for dissecting biological mechanisms, and a crucial step in this approach is to identify the molecular target responsible for a compounds activity. CGK733, a compound with anti-proliferative activity, was once reported as an ATM/ATR inhibitor, although this activity has been debated, and its target and mode of action have remained unclear. Here, we show that CGK733 inhibits cell-cycle progression and global protein translation. Affinity purification identified adenine nucleotide translocator 2 (ANT2) as the primary target. CGK733 blocked ATP export from mitochondria and induced proton leak, thereby shifting ATP production from mitochondrial respiration to glycolysis and perturbing the TCA cycle. These mitochondrial alterations were accompanied by inactivation of the mTOR pathway and mild activation of the integrated stress response, resulting in translational inhibition. Collectively, our findings demonstrate that CGK733 acts mainly through ANT2-dependent mitochondrial modulation, revealing a mechanistic link between mitochondrial bioenergetics and translational control.

biochemistry↗

Functional interplay between condensin I and topoisomerase IIα in single-molecule DNA compaction

Condensin I and topoisomerase II (topo II) are chromosomal ATPases essential for mitotic chromosome assembly. Mechanistically how the two ATPases cooperate to assemble mitotic chromosomes remains unknown. Here we use total internal reflection fluorescence microscopy to analyze the interplay between condensin I and topo II at single-molecule resolution. As observed in previous studies, condensin I alone predominantly forms DNA loops in an ATP-dependent manner. However, when topo II is included in the reaction, condensin I forms stable compact structures (termed "lumps") in a manner dependent on the C-terminal domain of topo II. Each of the stable lumps contains a single condensin I complex and a single topo II dimer. Remarkably, we find that topo II, when catalytically active, renders the lumps resistant to protease treatment. Several lines of evidence show that the protease-resistant lumps contain knotted DNA. A mutant condensin I complex defective in ATP hydrolysis, together with topo II, forms smaller lumps in which the probability of DNA knotting is greatly reduced. Our results demonstrate how topo II-mediated strand passage is coupled with condensin I-mediated loop extrusion to generate a compact DNA structure. Together with recent studies, we discuss the functional implications of these observations in mitotic chromosome assembly and stabilization.

molecular biology↗

Recombinant cyclin B-Cdk1-Suc1 capable of multi-site mitotic phosphorylation in vitro

Cyclin-dependent kinase 1 (Cdk1) complexed with cyclin B phosphorylates multiple sites on hundreds of proteins during mitosis. However, it is not fully understood how multi-site mitotic phosphorylation by cyclin B-Cdk1 controls the structures and functions of individual substrates. Here we develop an easy-to-use protocol to express recombinant vertebrate cyclin B and Cdk1 in insect cells from a single baculovirus vector and to purify their complexes with excellent homogeneity. A series of in-vitro assays demonstrate that the recombinant cyclin B-Cdk1 can efficiently and specifically phosphorylate the SP and TP motifs in substrates. The addition of Suc1 (a Cks1 homolog in fission yeast) accelerates multi-site phosphorylation of an artificial substrate containing TP motifs. Importantly, we show that mitosis-specific multi-subunit and multi-site phosphorylation of the condensin I complex can be recapitulated in vitro using recombinant cyclin B-Cdk1-Suc1. The materials and protocols described here will pave the way for dissecting the biochemical basis of critical mitotic processes that accompany Cdk1-mediated large-scale phosphorylation.

cell biology↗