Mechanism of DNA entrapment by the MukBEF SMC complex and its inhibition by a viral DNA mimic

Abstract

Ring-like structural maintenance of chromosomes (SMC) complexes are crucial for genome organization and operate through mechanisms of DNA entrapment and loop extrusion. Here, we explore the DNA loading process of the bacterial SMC complex MukBEF. Using electron cryomicroscopy (cryo-EM), we demonstrate that ATP binding opens one of MukBEFs three potential DNA entry gates, exposing a DNA capture site that positions DNA at the open neck gate. We discover that the gp5.9 protein of bacteriophage T7 blocks this capture site by DNA mimicry, thereby preventing DNA loading and inactivating MukBEF. We propose a comprehensive and unidirectional loading mechanism in which DNA is first captured at the complexs periphery and then ingested through the DNA entry gate, powered by a single cycle of ATP hydrolysis. These findings illuminate a fundamental aspect of how ubiquitous DNA organizers are primed for genome maintenance and demonstrate how this process can be disrupted by viruses. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=193 HEIGHT=200 SRC="FIGDIR/small/616235v1_ufig1.gif" ALT="Figure 1"> View larger version (68K): org.highwire.dtl.DTLVardef@165a949org.highwire.dtl.DTLVardef@14d1302org.highwire.dtl.DTLVardef@11afb6forg.highwire.dtl.DTLVardef@71694b_HPS_FORMAT_FIGEXP M_FIG C_FIG