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Plant and Cell Physiology Advance Access originally published online on January 16, 2008
Plant and Cell Physiology 2008 49(2):273-283; doi:10.1093/pcp/pcn003
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Significance of Zinc in a Regulatory Protein, CCM1, Which Regulates the Carbon-Concentrating Mechanism in Chlamydomonas reinhardtii

Tsutomu Kohinata, Haruku Nishino and Hideya Fukuzawa*

Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502 Japan

*Corresponding author: E-mail, fukuzawa{at}lif.kyoto-u.ac.jp; Fax, +81-75-753-6127.


  Abstract

In conditions with the poor availability of inorganic carbon (CO2 and HCO3 –: Ci) for photosynthesis, aquatic photosynthetic organisms induce active Ci uptake systems that allow accumulation of Ci within the cell, the so-called carbon-concentrating mechanism (CCM). In a unicellular green alga, Chlamydomonas reinhardtii, a regulatory factor CCM1 is indispensable for the regulation of the CCM by sensing CO2 availability. CCM1 has two putative zinc-binding domains with several conserved cysteine and histidine residues in its N-terminal region. To determine whether the domains actually bind zinc atoms, the N-terminal parts of CCM1 were expressed as glutathione S-transferase fusion proteins and subjected to atomic absorption spectrometry. It was found that 1 mol of zinc is bound to 1 mol of amino acid regions 1–71 and 72–101 of CCM1, respectively. In the case of the site-directed mutant proteins, H54Y, C77V and C80V, the zinc-binding ability was lost. Physiological analyses of the transgenic Chlamydomonas cells harboring a mutated Ccm1 gene revealed that amino acid residues such as C36, C41, H54, C77, C80, H90 and C93 were indispensable for induction of the CCM in response to Ci-limiting stress conditions. Size exclusion chromatography followed by immunoblot analyses indicated that CCM1 is present as a protein complex of approximately 290–580 kDa independent of Ci availability.

Keywords: Carbonic anhydrase — Carbon-concentrating mechanism — Carbon dioxide — Photosynthesis — Signal transduction — Zinc

Abbreviations: CA, carbonic anhydrase; CCM, carbon-concentrating mechanism; Ci, inorganic carbon; GST, glutathione S-transferase; high-CO2, 5% CO2-enriched air; HS, high salt; low-CO2, ordinary air containing 0.04% CO2; PBS, phosphate-buffered saline.

(Received November 22, 2007; Accepted December 27, 2007)
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