Mutational and Environmental Effects on the Dynamic Conformational Distributions of Lys48-Linked Ubiquitin Chains

Abstract

In multidomain proteins, individual domains connected by flexible linkers are dynamically rearranged upon ligand binding and sensing changes in environmental factors, such as pH and temperature. Here, we characterize dynamic domain rearrangements of Lys48-linked ubiquitin (Ub) chains as models of multidomain proteins in which molecular surfaces mediating intermolecular interactions are involved in intramolecular domain–domain interactions. Using NMR and other biophysical techniques, we characterized dynamic conformational interconversions of diUb between open and closed states regarding solvent exposure of the hydrophobic surfaces of each Ub unit, which serve as binding sites for various Ub-interacting proteins. We found that the hydrophobic Ub-Ub interaction in diUb was reinforced by cysteine substitution of Lys48 of the distal Ub unit because of interaction between the cysteinyl thiol group and the C-terminal segment of the proximal Ub unit. In contrast, the replacement of the isopeptide linker with an artificial ethylenamine linker minimally affected the conformational distributions. Furthermore, we demonstrated that the mutational modification allosterically impacted the exposure of the most distal Ub unit in triUb. Thus, the conformational interconversion of Ub chains offers a unique design framework in Ub-based protein engineering not only for developing biosensing probes but also for allowing new opportunities for the allosteric regulation of multidomain proteins.

Molecular Design of FRET Probes Based on Domain Rearrangement of Protein Disulfide Isomerase for Monitoring Intracellular Redox Status

“…In multidomain proteins, local perturbations such as ligand binding and site-directed mutation cause gross conformational changes accompanied by domain rearrangements, providing spectroscopic probes for monitoring intracellular environments as well as in vitro applications including drug screening [ 3 , 20 , 21 , 31 , 32 , 33 ]. Experimental and computational characterization of the conformational dynamics of multiple domains associated with fluorescence proteins is required to design effective biosensors.…”