Deubiquitinases deconjugate ubiquitin modifications from target proteins and are involved in many cellular processes in eukaryotes.? The functions of ?deubiquitinases are regulated by post-translational modifications (PTMs), mainly phosphorylation and ubiquitination. PTMs can result in subtle changes in structural and dynamic properties, which are difficult to identify but functionally important. In this work, we used NMR spectroscopy to characterize the conformational properties of the human deubiquitinase A (DUBA), a negative regulator of type I interferon. DUBA activity is regulated by phosphorylation at a single serine residue, Ser-177. We found that the catalytic rate constant of DUBA is enhanced by phosphorylation. By comparing NMR and enzyme kinetics data among different forms of DUBA with low and high activities, we concluded that a two-state equilibrium that was present only in phosphorylated DUBA is important for DUBA activity.Our results highlight the importance of defining conformational dynamics in understanding the mechanism of DUBA activation.,Published under license by The American Society for Biochemistry and Molecular Biology, Inc.