Unfolding ARF and ARL GTPases: from biophysics to systems-level insights.

Advanced technologies to study protein biophysics, mRNA expression and protein-protein interactions at high throughput in physiological or pathological contexts are reshaping our view of the ARF family of GTPases. Most current knowledge arises from work on the classical members ARF1 and ARF6, with many ARF-like proteins (ARLs) remaining poorly characterized. Recent findings suggest that several ARLs deviate from the binary molecular switch paradigm, instead exhibiting atypical biochemical properties, highly restricted tissue-specific expression patterns, specialized subcellular localizations, and unique interaction networks. These observations raise fundamental questions about the breadth of ARF family functions, mechanisms that regulate them, and their potential impact on cellular and organismal biology. In this review, we highlight emerging insights into atypical ARF members, outline unresolved questions, and discuss how expanding our understanding beyond the classical ARF members could shed light on their unique roles in health and disease.