Oxidative cyclization reagents reveal tryptophan cation-π interactions.

Methods for selective covalent modification of amino acids on proteins can enable a diverse array of applications, spanning probes and modulators of protein function to proteomics1-3. Owing to their high nucleophilicity, cysteine and lysine residues are the most common points of attachment for protein bioconjugation chemistry through acid-base reactivity3,4. Here we report a redox-based strategy for bioconjugation of tryptophan, the rarest amino acid, using oxaziridine reagents that mimic oxidative cyclization reactions in indole-based alkaloid biosynthetic pathways to achieve highly efficient and specific tryptophan labelling. We establish the broad use of this method, termed tryptophan chemical ligation by cyclization (Trp-CLiC), for selectively appending payloads to tryptophan residues on peptides and proteins with reaction rates that rival traditional click reactions and enabling global profiling of hyper-reactive tryptophan sites across whole proteomes. Notably, these reagents reveal a systematic map of tryptophan residues that participate in cation-π interactions, including functional sites that can regulate protein-mediated phase-separation processes.

An Activity-Based Oxaziridine Platform for Identifying and Developing Covalent Ligands for Functional Allosteric Methionine Sites: Redox-Dependent Inhibition of Cyclin-Dependent Kinase 4.

Activity-based protein profiling (ABPP) is a versatile strategy for identifying and characterizing functional protein sites and compounds for therapeutic development. However, the vast majority of ABPP methods for covalent drug discovery target highly nucleophilic amino acids such as cysteine or lysine. Here, we report a methionine-directed ABPP platform using Redox-Activated Chemical Tagging (ReACT), which leverages a biomimetic oxidative ligation strategy for selective methionine modification. Application of ReACT to oncoprotein cyclin-dependent kinase 4 (CDK4) as a representative high-value drug target identified three new ligandable methionine sites. We then synthesized a methionine-targeting covalent ligand library bearing a diverse array of heterocyclic, heteroatom, and stereochemically rich substituents. ABPP screening of this focused library identified 1oxF11 as a covalent modifier of CDK4 at an allosteric M169 site. This compound inhibited kinase activity in a dose-dependent manner on purified protein and in breast cancer cells. Further investigation of 1oxF11 found prominent cation-π and H-bonding interactions stabilizing the binding of this fragment at the M169 site. Quantitative mass-spectrometry studies validated 1oxF11 ligation of CDK4 in breast cancer cell lysates. Further biochemical analyses revealed cross-talk between M169 oxidation and T172 phosphorylation, where M169 oxidation prevented phosphorylation of the activating T172 site on CDK4 and blocked cell cycle progression. By identifying a new mechanism for allosteric methionine redox regulation on CDK4 and developing a unique modality for its therapeutic intervention, this work showcases a generalizable platform that provides a starting point for engaging in broader chemoproteomics and protein ligand discovery efforts to find and target previously undruggable methionine sites.

Cambios histológicos de la mucosa nasal en habitantes de la Ciudad de México en comparación con quienes no habitan en áreas metropolitanas / Histologic changes of the nasal mucosa in Mexico City's inhabitants versus inhabitants of suburban areas

Objetivo: Determinar cuáles son los cambios histopatológicos en la mucosa nasal de las personas que viven dentro del área metropolitana del Distrito Federal y que, por ende, están más expuestos a contaminantes ambientales inhalados, en comparación con un grupo control de sujetos que no habitan en áreas metropolitanas ni conurbadas. Material y métodos: Ciento veinte pacientes fueron incluidos en el estudio. Se integraron dos grupos: los que habitaban en el área metropolitana del D.F. (casos, n = 88) y sujetos que habitaran fuera de ella (controles, n = 32) que aceptaran por escrito participar en el estudio y que acudieran sin patología nasosinusal. Diseño: Prospectivo, comparativo, ciego, observacional y transversal. Parámetros de medición: Se revisó la morfología histológica en biopsias del epitelio proveniente del cornete inferior y si se podían relacionar los cambios metaplásicos con la exposición crónica a niveles elevados de contaminación atmosférica. Resultados: No se logró establecer una diferencia estadísticamente significativa que demostrara una clara correlación entre la exposición a contaminantes atmosféricos y la presencia de cambios metaplásicos en la mucosa nasal. Conclusiones: No es posible aseverar de manera estadísticamente significativa que la exposición a contaminantes inhalados por vivir en el área metropolitana de la Ciudad de México produce cambios histopatológicos en la mucosa nasal.