Editors' ChoiceBiochemistry

Single-molecule assay of ubiquitylation

Sci. Signal.  14 Apr 2015:
Vol. 8, Issue 372, pp. ec97
DOI: 10.1126/scisignal.aab3217

Many biological processes in cells are regulated by ubiquitin peptides that are attached to proteins. Measurement of single fluorescent molecules in cell extracts can be used to trace the kinetics of such reactions. Lu et al. refined assay conditions to follow ubiquitylation by an E3 ubiquitin ligase (see the Perspective by Komander). They visualized the activity of the anaphase-promoting complex (APC), a ubiquitin ligase critical for control of the cell division cycle. The processive initial reaction catalyzed by APC was replaced by slower reactions. The results show how small, commonly occurring recognition motifs can guide specific and highly controlled enzymatic events. In a companion paper, Lu et al. explored how the number and arrangement of added ubiquitin chains affected the interaction of ubiquitylated proteins with the proteasome (a protein complex that recognizes ubiquitylated proteins and degrades them). The extent of ubiquitylation determined the strength of interaction of a substrate protein with the proteasome, and the arrangement of the ubiquitin chains determined the movement of the protein into the proteasome and thus the rate of degradation.

Y. Lu, W. Wang, M. W. Kirschner, Specificity of the anaphase-promoting complex: A single-molecule study. Science 348, 1248737 (2015). [Abstract] [Full Text]

Y. Lu, B.-h. Lee, R. W. King, D. Finley, M. W. Kirschner, Substrate degradation by the proteasome: A single-molecule kinetic analysis. Science 348, 1250834 (2015). [Abstract] [Full Text]

D. Komander, Details of destruction, one molecule at a time. Science 348, 183–184 (2015). [Abstract] [Full Text]