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Appl Microbiol Biotechnol. 2008 Nov;81(1):69-78. doi: 10.1007/s00253-008-1623-y. Epub 2008 Aug 5.

A cyanophycin synthetase from Thermosynechococcus elongatus BP-1 catalyzes primer-independent cyanophycin synthesis.

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Department of Applied Chemistry, Faculty of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo, 169-8555, Japan.


Cyanophycin synthesis is catalyzed by cyanophycin synthetase (CphA). It was believed that CphA requires L-aspartic acid (Asp), L-arginine (Arg), ATP, Mg2+, and a primer (low-molecular mass cyanophycin) for cyanophycin synthesis and catalyzes the elongation of a low-molecular mass cyanophycin. Despite extensive studies of cyanophycin, the mechanism of primer supply is still unclear, and already-known CphAs were primer-dependent enzymes. In the present study, we found that recombinant CphA from Thermosynechococcus elongatus BP-1 (Tlr2170 protein) catalyzed in vitro cyanophycin synthesis in the absence of a primer. The Tlr2170 protein showed strict substrate specificity toward Asp and Arg. The optimum pH was 9.0, and Mg2+ or Mn2+ was essential for cyanophycin synthesis. KCl enhanced the cyanophycin synthesis activity of the Tlr2170 protein; in contrast, dithiothreitol did not. The Tlr2170 protein appeared to be a 400+/-9 kDa homo-tetramer. The Tlr2170 protein showed thermal stability and retained its 80% activity after a 60-min incubation at 50 degrees C. In addition, we examined cyanophycin synthesis at 30 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C. SDS-PAGE analysis showed that the molecular mass of cyanophycin increased with increased reaction temperature.

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