Biology subjects

Roisne-Hamelin, F.

Publications and source records attributed to Roisne-Hamelin, F..

3 recordsLinked to original sources

bioRxiv2024

4G cloning: rapid gene assembly for expression of multisubunit protein complexes in diverse hosts

Multi-subunit protein complexes are at the heart of many cellular processes, and studying their biochemical activities and structures in vitro requires their reconstitution by recombinant expression and purification. Obtaining targets at sufficient purity and scale typically requires the screening of several protein variants and expression hosts. Existing cloning strategies allow to produce constructs for co-expression of proteins, but are often time-consuming, labour-intensive, host-specific, or involving error-prone assembly steps. Here we present a unique set of vectors together with a novel assembly strategy designed to overcome these limitations. It allows for the generation of expression constructs for multi-subunit protein complexes for various hosts in a single cloning step. Its modular nature allows the system to be easily extended to target additional expression hosts or to include new tags or regulatory sequences. As a proof of principle, we present the parallel construction of expression vectors for several Structural Maintenance of Chromosomes (SMC) complexes, allowing us to devise strategies for the recombinant production of these targets in bacteria, insect cells, and human cells, respectively. This work will help laboratories working on protein complexes to streamline their workflow, increase their productivity and improve the quality of the purified material.

biochemistry↗

bioRxiv2023

Structural basis for plasmid restriction by SMC JET nuclease

DNA loop-extruding SMC complexes play crucial roles in chromosome folding and DNA immunity. Prokaryotic SMC Wadjet (JET) complexes limit the spread of circular plasmids through DNA cleavage; yet the mechanisms for target recognition are unresolved. We show that artificial DNA circularization renders linear DNA susceptible to JET cleavage. Unlike free DNA, JET cleaves immobilized plasmid DNA at a specific site, the plasmid-anchoring point, showing that the anchor hinders DNA extrusion but not DNA cleavage implying that residual unextruded DNA is cleaved. Structures of plasmid-bound JetABC reveal two presumably stalled SMC motor units that are drastically rearranged from the resting state, together entrapping a U-shaped DNA segment, which is further converted to kinked V-shaped cleavage substrate by JetD nuclease binding. Our findings uncover mechanical bending of residual unextruded DNA as principle for non-self DNA recognition and molecular signature for plasmid cleavage. We elucidate key elements of SMC loop extrusion including motor directionality and the structure of a DNA-holding state.

molecular biology↗

bioRxiv2022

DNA-measuring Wadjet SMC ATPases restrict smaller circular plasmids by DNA cleavage.

Structural maintenance of chromosomes (SMC) complexes fold DNA by loop extrusion to support chromosome segregation, genome maintenance, and gene expression. Wadjet systems (JetABCD/MksBEFG/EptABCD) are derivative SMC complexes with proposed roles in bacterial immunity against selfish DNA elements. Here, we show that JetABCD systems restrict extrachromosomal circular DNA with an upper size limit of about 100 kb, while a linear plasmid evades restriction. Recombinant preparations of a JetABCD complex cleave circular DNA regardless of its helical topology but not linear DNA; cleavage occurs at random positions and depends on ATP as well as the SMC ATPase. We solve a structure of the JetABCD core by cryo-EM revealing an alternative dimer-of-dimers configuration. The two SMC DNA motor units face in opposite orientations--rather than the same as observed with MukBEF--possibly representing a restriction-specific state of JetABCD. We hypothesize that JetABCD is a DNA-shape-specific endonuclease and present a model for the activation of DNA cleavage exclusively when extrusion of an entire plasmid has been completed by a single JetABCD complex. The self-stalling of two opposing DNA motor units may serve as signal to trigger DNA cleavage. Complete extrusion by a single complex cannot be achieved on the much larger chromosome, explaining how self-DNA may evade cleavage.

molecular biology↗