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Title: PROTEIN PHOSPHORYLATION AS A POSSIBLE TRIGGER FOR DEGRADATION OF METABOLIC ENZYMES

Author
item Huber, Steven
item TANG, G - NC STATE UNIV
item Hardin, Shane

Submitted to: Current Topics In Plant Biochemistry
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2002
Publication Date: 5/15/2003
Citation: HUBER, S.C., TANG, G.Q., HARDIN, S.C. 2003. Protein Phosphorylation As A Possible Trigger For Degradation of Metabolic Enzymes [abstract]. Current Topics In Plant Biochemistry, Physiology and Molecular Biology. Plant Protein Phosphorylation-Dephosphorylation. 21:1415.

Interpretive Summary:

Technical Abstract: The phosphorylation of a protein can affect its enzymatic activity, localization or interaction with other proteins. In addition, recent results suggest that phosphorylation of metabolic enzymes at certain sites might be a trigger for degradation via the ubiquitin/proteasome pathway. Recent results suggest this may be the case for maize sucrose synthase (Sus) phosphorylated at the Ser170 site and soybean cytosolic pyruvate kinase (PyrKinC) phosphorylated at Ser220 and Ser407. With Sus, phosphorylation of the major phosphorylation site at Ser15 affects the conformation of the N-terminus and may (or may not) influence the association of this soluble, globular protein with certain cellular membranes (Hardin et al., 2001). We have recently identified Ser170 as a second phosphorylation site on Sus. The Ser170 site is readily phosphorylated in vitro by CDPKs (but not a SnRK1-like protein kinase), but in vivo is only a minor site (low stoichiometry). We are speculating that endogenous binding proteins may attenuate the phosphorylation of Ser170 in vivo; this effect has been demonstrated with the ENOD40-encoded polypeptides in vitro. When phosphorylated, pS170 may function as part of a mechanism targeting Sus for proteasome-mediated degradation. Collectively, these results suggest that phosphorylation of plant enzymes can have multiple effects and that some phosphorylation sites (but not all) may represent "phospho-degrons," or phosphorylation events that target the protein for degradation.