Poster: Protein turnover

Abs # 816: A chloroplast protease, ClpP4, is a substrate of AtCHIP, an E3 ubiquitin ligase involved in stress response in plants

Presenter:	Shen, Guoxin , guoxin.shen@ttu.edu
Authors	Shen, Guoxin  (A)   Yan, Juqiang  (A)   Luo, Ester  (A)   Clarke, Adrian K. (B)   Zhang, Hong  (A)
Affiliations:	(A): Texas Tech University (B): Goteborg University

The Arabidopsis gene AtCHIP encodes a U-box-containing E3 ubiquitin ligase that plays a critical role in temperature stress tolerance [Plant Physiol., 132, 861-869]. Overexpression of AtCHIP leads to increased sensitivity to both high and low temperatures in Arabidopsis. To understand the molecular mechanism of AtCHIP’s involvement in temperature stresses, proteins that physically interact with AtCHIP were identified from yeast two-hybrid screening using AtCHIP as bait. One of the AtCHIP-interacting proteins identified is the nuclear-encoded chloroplast protease ClpP4, which belongs to a large family of ATP-dependent, Ser-type proteases found in chloroplast and bacteria. The Arabidopsis ClpP4 was expressed in bacterial cells, and purified ClpP4 protein was used for biochemical studies. ClpP4 could be ubiquitylated by AtCHIP in vitro, which not only confirms the protein-protein interaction data from yeast two-hybrid screening, but also indicates that ClpP4 might be AtCHIP’s in vivo substrate. Since ClpP4 is part of a major protein-degradation machinery in chloroplast stroma, its ubiquitylation by AtCHIP suggests that protein degradation in chloroplast is regulated by AtCHIP, indicating that AtCHIP plays important roles in protein quality control, not only in protein turnover metabolism in cytoplasm, but also in protein turnover metabolism in chloroplast.