Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Biochemistry. 2010 Aug 24;49(33):7000-11. doi: 10.1021/bi100463d.
Cyanobacterium Synechococcus sp. PCC 7002 contains a single gene (glbN) coding for GlbN, a protein of the 2/2 hemoglobin lineage. The precise function of GlbN is not known, but comparison to similar 2/2 hemoglobins suggests that reversible dioxygen binding is not its main activity. In this report, the results of in vitro and in vivo experiments probing the role of GlbN are presented. Transcription profiling indicated that glbN is not strongly regulated under any of a large number of growth conditions and that the gene is probably constitutively expressed. High levels of nitrate, used as the sole source of nitrogen, and exposure to nitric oxide were tolerated better by the wild-type strain than a glbN null mutant, whereas overproduction of GlbN in the null mutant background restored the wild-type growth. The cellular contents of reactive oxygen/nitrogen species were elevated in the null mutant under all conditions and were highest under NO challenge or in the presence of high nitrate concentrations. GlbN overproduction attenuated these contents significantly under the latter conditions. The analysis of cell extracts revealed that the heme of GlbN was covalently bound to overproduced GlbN apoprotein in cells grown under microoxic conditions. A peroxidase assay showed that purified GlbN does not possess significant hydrogen peroxidase activity. It was concluded that GlbN protects cells from reactive nitrogen species that could be encountered naturally during growth on nitrate or under denitrifying conditions. The solution structure of covalently modified GlbN was determined and used to rationalize some of its chemical properties.
聚球藻 PCC 7002 含有一个单一的基因（glbN），编码 GlbN，一种 2/2 血红蛋白家族的蛋白质。GlbN 的精确功能尚不清楚，但与类似的 2/2 血红蛋白相比，表明可逆的双氧结合不是其主要活性。本报告介绍了体外和体内实验探测 GlbN 作用的结果。转录谱分析表明，glbN 在大量生长条件下都没有被强烈调控，而且该基因可能是组成型表达的。高浓度的硝酸盐（用作唯一氮源）和一氧化氮暴露比 glbN 缺失突变体更能耐受野生型菌株，而在缺失突变体背景中过量表达 GlbN 则恢复了野生型生长。在所有条件下，缺失突变体的细胞内活性氧/氮物质含量升高，在 NO 挑战或高硝酸盐浓度存在下最高。在后者条件下，GlbN 的过表达显著降低了这些含量。对细胞提取物的分析表明，在微氧条件下生长的细胞中，GlbN 的血红素与过表达的 GlbN 脱辅基蛋白共价结合。过氧化物酶测定表明，纯化的 GlbN 没有显著的过氧化氢酶活性。因此得出结论，GlbN 保护细胞免受在硝酸盐生长或反硝化条件下自然遇到的活性氮物质的侵害。确定了共价修饰的 GlbN 的溶液结构，并用于合理化其一些化学性质。
