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Microbiology 155 (2009), 1427-1439; DOI  10.1099/mic.0.026351-0
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Microbiology 155 (2009), 1427-1439; DOI  10.1099/mic.0.026351-0
© 2009 Society for General Microbiology

An alternative methionine aminopeptidase, MAP-A, is required for nitrogen starvation and high-light acclimation in the cyanobacterium Synechocystis sp. PCC 6803

Miriam Drath1, Kerstin Baier2 and Karl Forchhammer1,3

1 Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany
2 Institut für Biologie, Humboldt-Universität zu Berlin, 10115 Berlin, Germany
3 Institut für Mikrobiologie, Eberhard-Karls-Universität Tübingen, 72076 Tübingen, Germany

Methionine aminopeptidases (MetAPs or MAPs, encoded by map genes) are ubiquitous and pivotal enzymes for protein maturation in all living organisms. Whereas most bacteria harbour only one map gene, many cyanobacterial genomes contain two map paralogues, the genome of Synechocystis sp. PCC 6803 even three. The physiological function of multiple map paralogues remains elusive so far. This communication reports for the first time differential MetAP function in a cyanobacterium. In Synechocystis sp. PCC 6803, the universally conserved mapC gene (sll0555) is predominantly expressed in exponentially growing cells and appears to be a housekeeping gene. By contrast, expression of mapA (slr0918) and mapB (slr0786) genes increases during stress conditions. The mapB paralogue is only transiently expressed, whereas the widely distributed mapA gene appears to be the major MetAP during stress conditions. A mapA-deficient Synechocystis mutant shows a subtle impairment of photosystem II properties even under non-stressed conditions. In particular, the binding site for the quinone QB is affected, indicating specific N-terminal methionine processing requirements of photosystem II components. MAP-A-specific processing becomes essential under certain stress conditions, since the mapA-deficient mutant is severely impaired in surviving conditions of prolonged nitrogen starvation and high light exposure.

Correspondence
Karl Forchhammer
karl.forchhammer{at}uni-tuebingen.de

Abbreviations: Chla, chlorophyll a; DCBQ, 2,6-dichloro-p-benzoquinone; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea; MetAP, methionine aminopeptidase; MmapA, mapA mutant; NME; N-terminal methionine excision; PAM, pulse amplitude modulated; PQQ, phenyl-p-quinone; PSII, photosystem II; RACE, rapid amplification of 5' cDNA ends

Two supplementary figures are available with the online version of this paper.






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