Toll-like receptors (TLRs) belong to a class of pattern-recognition receptors that play an important role in host defense against pathogens by recognizing a wide variety of pathogen-associated molecular patterns (PAMPs). Besides driving inflammatory responses, TLRs also regulate cell proliferation and survival by expanding useful immune cells and integrating inflammatory responses and tissue repair processes. TLR signaling, which is centrally involved in the initiation of both innate and adaptive immune responses, has been thought to be restricted to immune cells. However, recent studies have shown that functional TLRs are expressed not only on immune cells, but also on cancer cells, thus implicating a role of TLRs in tumor biology. Increasing bodies of evidence have suggested that TLRs act as a double-edged sword in cancer cells because uncontrolled TLR signaling provides a microenvironment that is necessary for tumor cells to proliferate and evade the immune response. Alternatively, TLRs can induce an antitumor immune response in order to inhibit tumor progression. In this review, we summarize the dual roles of TLRs in tumor cells and, more importantly, delve into the therapeutic potential of TLRs in the context of tumorigenesis.

Metabolic labeling of proteins with the methionine (1) surrogate azidonorleucine (2) can be targeted exclusively to specified cells through expression of a mutant methionyl-tRNA synthetase (MetRS). In complex cellular mixtures, proteins made in cells that express the mutant synthetase can be tagged with affinity reagents (for detection or enrichment) or fluorescent dyes (for imaging). Proteins made in cells that do not express the mutant synthetase are neither labeled nor detected.

directed evolution ͉ noncanonical amino acids ͉ protein engineering

Intrinsically disordered proteins (IDPs), which play key roles in cell signaling and regulation, do not display specific tertiary structure when isolated in solution. Instead, they dynamically explore an ensemble of unfolded configurations, adopting more stable, ordered structures only after binding to their ligands. Whether ligands induce IDP structural changes upon binding or simply bind to pre-existing conformers that are populated within the IDP's structural ensemble is not well understood. Molecular simulations can provide information with the spatiotemporal resolution necessary to resolve these issues. Here, we report on the conformational ensemble of a 15-residue wild-type p53 fragment from the TAD domain and its mutant (TAD-P27L) obtained by replica exchange molecular dynamics simulation using an optimized (fully atomistic, explicit solvent) protein model and the experimental validation of the simulation results. We use a clustering method based on structural similarity to identify conformer states populated by the peptides in solution from the simulated ensemble. We show that p53 populates solution structures that strongly resemble the ligand (MDM2)-bound structure, but at the same time, the conformational free-energy landscape is relatively flat in the absence of the ligand.