Commentary

The pharmaceutical industry continues to experience significant attrition of drug candidates during phase 2 proof-of-concept clinical studies. We describe some questions about the characteristics of protein targets and small-molecule drugs that may be important to consider in drug-discovery projects and could improve prospects for future clinical success.

Protein aggregation is a central hallmark of many neurodegenerative disorders, but the relationship of aggregate structural diversity to the resultant cellular cytotoxicity and phenotypic diversity has remained obscure. Recent advances in understanding the mechanisms of protein aggregation and their physiological consequences have been achieved through chemical biology approaches, such as rationally designed protein modifications and chemical probes, providing crucial mechanistic insights and promise for therapeutic strategies for brain disorders.

The ubiquitin-proteasome system (UPS) pervades the biology of eukaryotes. Because it depends on the activity of hundreds of different enzymes and protein-protein interactions, the UPS provides many opportunities for selective modulation of the pathway with small molecules. Here we discuss the principles that underlie the development of effective inhibitors or activators of the pathway. We emphasize insights from structural analysis and describe strategies for evaluating the selectivity of compounds.

Biotechnology is a central focus in efforts to provide sustainable solutions for the provision of fuels, chemicals and materials. On the basis of a recent open discussion, we summarize the development of this field, highlighting the distinct but complementary approaches provided by metabolic engineering and synthetic biology for the creation of efficient cell factories to convert biomass and other feedstocks to desired chemicals.

Peptides fulfill many roles in immunology, yet none are more important than their role as immunogenic epitopes driving the adaptive immune response, our ultimate bulwark against infectious disease. Peptide epitopes are mediated primarily by their interaction with major histocompatibility complexes (T-cell epitopes) and antibodies (B-cell epitopes). As pathogen genomes continue to be revealed, both experimental and computational epitope mapping are becoming crucial tools in vaccine discovery^1,2. Immunoinformatics offers many tools, techniques and approaches for in silico epitope characterization, which is capable of greatly accelerating epitope design.

Genetic code expansion for synthesis of proteins containing noncanonical amino acids is a rapidly growing field in synthetic biology. Creating optimal orthogonal translation systems will require re-engineering central components of the protein synthesis machinery on the basis of a solid mechanistic biochemical understanding of the synthetic process.

The recent development of a broad range of biocatalysts that can be applied in organic synthesis has brought into focus the need to rethink the way in which organic target molecules might be constructed in the future. To aid synthetic chemists in identifying where biocatalysts might be usefully applied, we propose that guidelines and rules for 'biocatalytic retrosynthesis' be developed and that this new approach be embedded in the future training and education of organic chemists.

Small-molecule phenotypic screening has high potential in the discovery of new chemical probes and new biological small-molecule targets. This commentary will discuss the basic principles underlying the design of phenotypic screens and propose some guidelines to facilitate the discovery of small molecules from phenotypic screens.

Providing chemical matter to modulate newly identified biological targets—as well as pre-existing but chemically intractable ones—remains a challenge in the discovery of therapeutics. Here, we discuss opportunities for synthetic chemists to make a direct impact in addressing targets that are considered 'undruggable'.

Fully profiled chemical probes are essential to support the unbiased interpretation of biological experiments necessary for rigorous preclinical target validation. We believe that by developing a 'chemical probe tool kit', and a framework for its use, chemical biology can have a more central role in identifying targets of potential relevance to disease, avoiding many of the biases that complicate target validation as practiced currently.

Chemical probes are critical tools for elucidating the biological functions of proteins and can lead to new medicines for treating disease. The pharmacological validation of protein function requires verification that chemical probes engage their intended targets in vivo. Here we discuss technologies, both established and emergent, for measuring target engagement in living systems and propose that determining this parameter should become standard practice for chemical probe and drug discovery programs.

Chemical probes are urgently needed to functionally annotate hitherto-untargeted kinases and stimulate new drug discovery efforts to address unmet medical needs. The size of the human kinome combined with the high cost associated with probe generation severely limits access to new probes. We propose a large-scale public-private partnership as a new approach that offers economies of scale, minimized redundancy and sharing of risk and cost.

G protein–coupled receptors (GPCRs) are versatile molecular machines that regulate the majority of physiological responses to chemically diverse hormones and neurotransmitters. Recent breakthroughs in structural studies have advanced our understanding of GPCR signaling, particularly the selectivity of ligand recognition and receptor activation of G proteins.

Defining G protein–coupled receptor ligand efficacy and biased agonism in precise chemical terms is one challenge posed by the current structural data that exists for this receptor family. Concepts classically used for understanding enzymes and other nonreceptor proteins may lead us in the right direction.

Intrinsically disordered proteins and complex multidomain proteins are characterized by a dynamic ensemble of conformations that cannot be unequivocally described by traditional static terms of structural biology. The functional importance of this structural complexity necessitates new standards and protocols for the description and deposition of such 'supertertiary' structural ensembles into structural databases.

Learning metabolism inevitably involves memorizing pathways. The teacher's challenge is to motivate memorization and to help students progress beyond it. To this end, students should be taught a few fundamental chemical reaction mechanisms and how these are repeatedly used to achieve pathway goals. Pathway knowledge should then be reinforced through quantitative problems that emphasize the relevance of metabolism to bioengineering and medicine.

A growing body of evidence points to the importance of microcolonies in the dissemination of bacteria, yet there is a dearth of tools for systematically assessing the behavior of cells within such communities. New strategies for landscaping three-dimensional culture environments on microscopic scales may have a critical role in revealing how bacteria orchestrate antibiotic resistance and other social behaviors within small, dense aggregates.

Despite our continued efforts to assert control over pathogens, more and more bacteria are saying “no” to drugs. It is becoming increasingly apparent that microbial environments, influenced by intracellular and extracellular metabolic processes, modulate antibiotic susceptibility in bacteria. A deeper understanding of these environmental processes may prove crucial for the development of new antibacterial therapies.

The distinction between different cell-envelope architectures has defined much of our thinking about bacterial systematics, but the evolution of different envelope layers has been harder to understand. A recent publication focused on the non-model organism Acetonema longum provides important clues to the possible origin of the second membrane typical of Gram-negative bacteria.

Antibiotics promote the spread of resistance in the clinic, but various mechanisms may exist in natural environments that tilt the balance toward antibiotic sensitivity. Studying such mechanisms could help us understand the evolutionary dynamics of resistance and sensitivity in the wild, which may inspire new therapeutic strategies.