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Journal of Biochemistry Advance Access published online on May 18, 2009
Journal of Biochemistry, doi:10.1093/jb/mvp073
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© The authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.

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Protein Quality Control in Chloroplasts: a Current Model of D1 Protein Degradation in the Photosystem II Repair Cycle

Yusuke Kato and Wataru Sakamoto

Research Institute for Bioresources, Okayama University

Corresponding author: Wataru Sakamoto Mailing address: Research Institute for Bioresources Okayama University 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan Telephone number: 81-86-434-1206 Fax number: 81-86-434-1206 E-mail: saka{at}rib.okayama-u.ac.jp

Received March 11, 2009; Accepted March 27, 2009


  Abstract

The chloroplast originated from endosymbiosis of photosynthetic bacteria. Thus, mechanisms essential for chloroplast biogenesis/homeostasis (protein synthesis, import from cytosol, assembly, and degradation) are predominantly governed by prokaryotic systems. Among these, the quality control system is crucial, because light energy constantly damages photosynthetic proteins and excessive light often limits plant growth by irreversibly inactivating the photosynthetic apparatuses. Here, we overview prokaryotic proteases (FtsH and Deg) which are two enzymes that play critical roles in this system. We particularly focus on Photosystem II (PSII) in thylakoid membranes, which is composed by more than 20 subunits. Among the subunits is one of the intrinsic reaction center proteins (D1) which is considered to be the target of photodamage. Its rapid and specific turnover suggests that photodamaged D1 is degraded by these proteases and replaced with a de novo synthesized one in a system which is termed the PSII repair cycle. We discuss a current model of D1 degradation which is executed by a concerted action of particular FtsH and Deg isoforms.

Key Words: chloroplast, D1 degradation, Deg protease, FtsH metalloprotease, photosynthesis


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