Metal-Mediated Functionalization of Natural Peptides and Proteins: Panning for Bioconjugation Gold.

Selective modification of natural proteins is a daunting methodological challenge and a stringent test of selectivity and reaction scope. There is a continued need for new reactivity and new selectivity concepts. Transition metals exhibit a wealth of unique reactivity that is orthogonal to biological reactions and processes. As such, metal-based methods play an increasingly important role in bioconjugation. This Review examines metal-based methods as well as their reactivity and selectivity for the functionalization of natural proteins and peptides.

A Vinylogous Photocleavage Strategy Allows Direct Photocaging of Backbone Amide Structure.

Side-chain modifications that respond to external stimuli provide a convenient approach to control macromolecular structure and function. Responsive modification of backbone amide structure represents a direct and powerful alternative to impact folding and function. Here, we describe a new photocaging method using histidine-directed backbone modification to selectively modify peptides and proteins at the amide N-H bond. A new vinylogous photocleavage method allows photorelease of the backbone modification and, with it, restoration of function.

Designing Selectivity in Dirhodium Metallopeptide Catalysts for Protein Modification.

The ability to chemically alter proteins is important for broad areas of chemical biology, biophysics, and medicine. Chemical catalysts for protein modification, and particularly rhodium(II) conjugates, represent an important new approach to protein modification that develops novel functionalization approaches while shedding light on the development of selective chemistries in complex environments. Here, we elucidate the reaction parameters that allow selective catalysis and even discrimination among highly similar proteins. Furthermore, we show that quantifying modification allows the measurement of competitive ligand affinity, permitting straightforward measurement of protein-peptide interactions and inhibitors thereof. Taken as a whole, rhodium(II) conjugates replicate many features of enzymes in an entirely chemical construct.

ADAM8 signaling drives neutrophil migration and ARDS severity.

Acute respiratory distress syndrome (ARDS) results in catastrophic lung failure and has an urgent, unmet need for improved early recognition and therapeutic development. Neutrophil influx is a hallmark of ARDS and is associated with the release of tissue-destructive immune effectors, such as matrix metalloproteinases (MMPs) and membrane-anchored metalloproteinase disintegrins (ADAMs). Here, we observed using intravital microscopy that Adam8-/- mice had impaired neutrophil transmigration. In mouse pneumonia models, both genetic deletion and pharmacologic inhibition of ADAM8 attenuated neutrophil infiltration and lung injury while improving bacterial containment. Unexpectedly, the alterations of neutrophil function were not attributable to impaired proteolysis but resulted from reduced intracellular interactions of ADAM8 with the actin-based motor molecule Myosin1f that suppressed neutrophil motility. In 2 ARDS cohorts, we analyzed lung fluid proteolytic signatures and identified that ADAM8 activity was positively correlated with disease severity. We propose that in acute inflammatory lung diseases such as pneumonia and ARDS, ADAM8 inhibition might allow fine-tuning of neutrophil responses for therapeutic gain.

Aminoquinoline-Rhodium(II) Conjugates as Src-Family SH3 Ligands.

High-affinity, selective ligands are sought for a variety of biomolecules but are particularly difficult to generate in the protein-protein interaction space. Rhodium(II) conjugates provide a structure-based approach to improved affinity and specificity for targeting protein-protein interactions such as SH3 domains. In this study of small-molecule-rhodium conjugates, we report a potent ligand 4b (K d of 27 nM) for the Lyn SH3 domain, based on an aminoquinoline fragment. The results demonstrate robust affinity gains possible from even modest small-molecule leads through cooperative inorganic-organic binding, based on specific histidine interactions. A docking study sheds light on the structural basis of binding and supports a previously proposed binding model.