Morad, V. | Search bioRxiv

bioRxiv2024

Structural characterization of the Pseudomonas Aeruginosa MexR-mexR repressor-operator complex: a small-angle X-ray and neutron scattering perspective

The rapid spread of acquired multidrug resistance (MDR) in bacteria is a world-wide health threat. The MexR protein regulates the expression of the MexAB-OprM efflux pump, which actively extrudes chemical compounds with high toxicity to the host organism Pseudomonas Aeruginosa. In repression mode, two MexR dimers bind to an operator with two homologous pseudo-palindromic boxes located in proximity (named PI and PII). Here we report a first structural characterization of the complex in solution using small angle X-ray scattering (SAXS), small-angle neutron scattering (SANS) and rigid body modelling. The spacing between the PI and PII boxes is rich in AT base pairs indicate possible flexibility between the two MexR dimer binding sites. In agreement, our best modelling fits show a requirement for DNA bending between the two MexR binding sites to optimally fit SAS data as well as known biological properties of the MexR operons. Taken together, this study contributes to better understanding of the structural properties of bacterial operators and their repressor proteins.

biophysics↗

bioRxiv2021

The PNUTS-PAD domain recruits MYC to the PNUTS:PP1 phosphatase complex via the oncogenic MYC-MB0 region

Despite MYC dysregulation in most human cancers, strategies to target this potent oncogenic driver remains an urgent unmet need. Recent evidence shows the PP1 phosphatase and its regulatory subunit PNUTS control MYC phosphorylation and stability, however the molecular basis remains unclear. Here we demonstrate that MYC interacts directly with PNUTS through the MYC homology Box 0 (MB0), a highly conserved region recently shown to be important for MYC oncogenic activity. MB0 interacts with PNUTS residues 1-148, a functional unit here termed, PNUTS amino-terminal domain (PAD). Using NMR spectroscopy we determined the solution structure of PAD, and characterised its interaction with MYC. Point mutations of residues at the MYC-PNUTS interface significantly weaken their interaction both in vitro and in vivo. These data demonstrate the MB0 binding pocket of the PAD represents an attractive site for pharmacological disruption of the MYC-PNUTS interaction. In BriefSolving the structure of MYC-PNUTS direct interaction reveals how the intrinsically disordered MYC-Box0 (MB0) region anchors into a binding pocket in the N-terminal PAD domain of PNUTS. These data provide insight into the molecular mechanism of how the PNUTS:PP1 phosphatase complex regulates MYC phosphorylation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=197 SRC="FIGDIR/small/470928v1_ufig1.gif" ALT="Figure 1"> View larger version (86K): org.highwire.dtl.DTLVardef@179b89corg.highwire.dtl.DTLVardef@47338eorg.highwire.dtl.DTLVardef@89b6f4org.highwire.dtl.DTLVardef@14a80bd_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIA region critical for MYC oncogenesis, MYC-Box0 (MB0), directly interacts with PNUTS C_LIO_LIPNUTS amino-terminal domain (PAD) is a structural domain that interacts with MYC MB0 C_LIO_LIMutation of single residues at the interaction interface disrupts MYC-PNUTS binding in cells C_LIO_LIMYC-PNUTS binding releases MYC intramolecular interactions to enable PP1substrate access C_LI

cancer biology↗