State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, China.
FEMS Microbiol Lett. 2009 Aug;297(1):17-23. doi: 10.1111/j.1574-6968.2009.01644.x. Epub 2009 May 8.
HetN, a putative ketoacyl reductase, is required for heterocyst pattern maintenance in the filamentous cyanobacterium Anabaena sp. strain PCC 7120. The hetN gene, when present on a multicopy plasmid, is able to suppress heterocyst differentiation. Little is known about the biochemical properties of HetN. In the present study, we found that HetN could hydrolyze ATP or GTP in vitro, and that this activity was dependent on the presence of magnesium in the reaction mixture. Mutations of the conserved active Ser(142)-Tyr(155)-Lys(159) triad, predicted as necessary for the reductase activity of HetN, had only weak effect on the hydrolysis of ATP. The residue Lys(159) is shown to be necessary for the heterocyst-suppressing activity of HetN, as the corresponding mutant allele present on a replicative plasmid failed to block heterocyst differentiation in contrast to the wild type. This result suggests that the reductase activity of HetN is involved in the HetN-mediated inhibition of heterocyst formation.
HetN 是一种假定的酮酰还原酶，对于丝状蓝藻鱼腥藻 PCC 7120 中异形胞模式的维持是必需的。HetN 基因存在于多拷贝质粒上时，能够抑制异形胞分化。关于 HetN 的生化特性知之甚少。在本研究中，我们发现 HetN 可以在体外水解 ATP 或 GTP，并且该活性依赖于反应混合物中镁的存在。预测为 HetN 还原酶活性所必需的保守活性 Ser(142)-Tyr(155)-Lys(159)三联体的突变对 ATP 的水解只有微弱的影响。赖氨酸残基 159 对于 HetN 的异形胞抑制活性是必需的，因为与野生型相比，存在于复制质粒上的相应突变等位基因未能阻断异形胞分化。这一结果表明，HetN 的还原酶活性参与了 HetN 介导的异形胞形成抑制。
