Molecule of the Month: Auxin and TIR1 Ubiquitin Ligase
The plant hormone auxin controls growth and response to light and gravity
Auxin in Action
Exploring the Structure
Auxin and TIR1 Ubiquitin Ligase (PDB entry 2p1q)
The structure of auxin bound to the ubiquitin ligase revealed other surprises. Auxin promotes the binding of Aux/IAA proteins to the ligase, leading to their destruction, but it doesn't do this by changing the shapes of the proteins. Instead, it acts as molecular glue that bridges the two molecules. Auxin binds in a deep pocket in ubiquitin ligase, filling in a hole and creating a surface that perfectly matches the Aux/IAA protein. In this structure, from PDB entry 2p1q , auxin (in green) is bound to the ligase (in blue), and a short peptide from Aux/IAA (in magenta) is layered on top of the complex.
Topics for Further Discussion
- Auxin is composed of an acidic group and an aromatic indole ring. How are these chemical groups recognized by the active site of TIR1 ubiquitin ligase?
- Structures of auxin-binding protein 1, a protein that also binds tightly to auxin, are available in the PDB. Does it use a similar collection of amino acids to recognize auxin in its binding site?
Related PDB-101 Resources
- Browse Cellular Signaling
- Browse Biotechnology
- Browse Biology of Plants
- K. Mockaitis and M. Estelle (2008) Auxin receptors and plant development: a new signaling paradigm. Annual Review of Cell and Developmental Biology 24, 55-80.
- C. Perrot-Rechenmann and R. M. Napier (2005) Auxins. Vitamins and Hormones 72, 203-233. H.W. Heldt (1997) Plant biochemistry and molecular biology. Oxford University Press.
February 2009, David Goodselldoi:10.2210/rcsb_pdb/mom_2009_2