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New chemical probes could help researchers investigate how RAB27 proteins control intracellular trafficking and contribute to disease

Researchers at Imperiaand collaborating institutions, led by Tate group members including Dr Elena De Vita and Dr Adam Thomas, have developed the first cell-active, rationally designed covalent inhibitors of the RAB27-effector protein–protein interaction.

, the study describes a new approach to targeting RAB27A and RAB27B — small GTPases that regulate the movement of vesicles inside cells. These proteins are involved in endocytic and exocytic processes, with implications for cellular communication, immune responses, tumour metastasis and chronic inflammation.

Small GTPases have historically been challenging drug targets. Their conserved GTP-binding sites offer limited selectivity, while the broad surfaces used to bind effector proteins are difficult to disrupt with conventional small molecules.

The team addressed this challenge by combining an electrophile-first biochemical screen with structure-guided drug design. This led to a new class of acrylamide-based covalent inhibitors that target a non-conserved cysteine residue, Cys123, positioned close to the RAB27-effector interaction interface.

X-ray crystallography helped guide the optimisation of the compounds, while biochemical and cellular experiments showed that the most effective probes selectively target RAB27A and RAB27B in cells. Chemical-proteomic studies further supported their selectivity, and experiments in melanocytes demonstrated that the compounds could reproduce cellular effects associated with disrupting RAB27 function.

The researchers also tested Nexinhib-20, a previously reported RAB27 inhibitor. Their results indicated that the compound was cytotoxic and acted through non-selective reactivity, highlighting the importance of carefully validating chemical probes used to study protein function.

The study provides a toolbox of selective, cell-active RAB27 probes, including a matched inactive enantiomeric control. These reagents will enable further investigation of RAB27 biology and could help assess whether the protein–protein interaction is a viable target for future therapeutic development.

Congratulations to everyone involved in this publication!