Light-Fueled Primitive Replication and Selection in Biomimetic Chemical Systems

The concept of chemically evolvable replicators is centralto abiogenesis.Chemical evolvability requires three essential components: energy-harvestingmechanisms for nonequilibrium dissipation, kinetically asymmetricreplication and decomposition pathways, and structure-dependent selectivetemplating in the autocatalytic cycles. We observed a UVA light-fueledchemical system displaying sequence-dependent replication and replicatordecomposition. The system was constructed with primitive peptidicfoldamer components. The photocatalytic formation-recombinationcycle of thiyl radicals was coupled with the molecular recognitionsteps in the replication cycles. Thiyl radical-mediated chain reactionwas responsible for the replicator death mechanism. The competingand kinetically asymmetric replication and decomposition processesled to light intensity-dependent selection far from equilibrium. Here,we show that this system can dynamically adapt to energy influx andseeding. The results highlight that mimicking chemical evolution isfeasible with primitive building blocks and simple chemical reactions

A Series of Xanthenes Inhibiting Rad6 Function and Rad6–Rad18 Interaction in the PCNA Ubiquitination Cascade

Ubiquitination of proliferating cell nuclear antigen (PCNA) triggers pathways of DNA damage tolerance, including mutagenic translesion DNA synthesis, and comprises a cascade of reactions involving the E1 ubiquitin-activating enzyme Uba1, the E2 ubiquitin-conjugating enzyme Rad6, and the E3 ubiquitin ligase Rad18. We report here the discovery of a series of xanthenes that inhibit PCNA ubiquitination, Rad6∼ubiquitin thioester formation, and the Rad6–Rad18 interaction. Structure-activity relationship experiments across multiple assays reveal chemical and structural features important for different activities along the pathway to PCNA ubiquitination. The compounds that inhibit these processes are all a subset of the xanthen-3-ones we tested. These small molecules thus represent first-in-class probes of Rad6 function and the association of Rad6 and Rad18, the latter being a new inhibitory activity discovered for a small molecule, in the PCNA ubiquitination cascade and potential therapeutic agents to contain cancer progression

Structural Adaptation of the Single-Stranded DNA-Binding Protein C-Terminal to DNA Metabolizing Partners Guides Inhibitor Design

Single-stranded DNA-binding protein (SSB) is a bacterial interaction hub and an appealing target for antimicrobial therapy. Understanding the structural adaptation of the disordered SSB C-terminus (SSB-Ct) to DNA metabolizing enzymes (e.g., ExoI and RecO) is essential for designing high-affinity SSB mimetic inhibitors. Molecular dynamics simulations revealed the transient interactions of SSB-Ct with two hot spots on ExoI and RecO. The residual flexibility of the peptide–protein complexes allows adaptive molecular recognition. Scanning with non-canonical amino acids revealed that modifications at both termini of SSB-Ct could increase the affinity, supporting the two-hot-spot binding model. Combining unnatural amino acid substitutions on both segments of the peptide resulted in enthalpy-enhanced affinity, accompanied by enthalpy–entropy compensation, as determined by isothermal calorimetry. NMR data and molecular modeling confirmed the reduced flexibility of the improved affinity complexes. Our results highlight that the SSB-Ct mimetics bind to the DNA metabolizing targets through the hot spots, interacting with both of segments of the ligands