Hill D R, Belbin T J, Thorsteinsson M V, Bassam D, Brass S, Ernst A, Böger P, Paerl H, Mulligan M E, Potts M
Department of Biochemistry and Anaerobic Microbiology, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Bacteriol. 1996 Nov;178(22):6587-98. doi: 10.1128/jb.178.22.6587-6598.1996.
The glbN gene of Nostoc commune UTEX 584 is juxtaposed to nifU and nifH, and it encodes a 12-kDa monomeric hemoglobin that binds oxygen with high affinity. In N. commune UTEX 584, maximum accumulation of GlbN occurred in both the heterocysts and vegetative cells of nitrogen-fixing cultures when the rate of oxygen evolution was repressed to less than 25 micromol of O2 mg of chlorophyll a(-1) h(-1). Accumulation of GlbN coincided with maximum synthesis of NifH and ferredoxin NADP+ oxidoreductase (PetH or FNR). A total of 41 strains of cyanobacteria, including 40 nitrogen fixers and representing 16 genera within all five sections of the cyanobacteria were screened for the presence of glbN or GlbN. glbN was present in five Nostoc strains in a single copy. Genomic DNAs from 11 other Nostoc and Anabaena strains, including Anabaena sp. strain PCC 7120, provided no hybridization signals with a glbN probe. A constitutively expressed, 18-kDa protein which cross-reacted strongly with GlbN antibodies was detected in four Anabaena and Nostoc strains and in Trichodesmium thiebautii. The nifU-nifH intergenic region of Nostoc sp. strain MUN 8820 was sequenced (1,229 bp) and was approximately 95% identical to the equivalent region in N. commune UTEX 584. Each strand of the DNA from the nifU-nifH intergenic regions of both strains has the potential to fold into secondary structures in which more than 50% of the bases are internally paired. Mobility shift assays confirmed that NtcA (BifA) bound a site in the nifU-glbN intergenic region of N. commune UTEX 584 approximately 100 bases upstream from the translation initiation site of glbN. This site showed extensive sequence similarity with the promoter region of glnA from Synechococcus sp. strain PCC 7942. In vivo, GlbN had a specific and prominent subcellular location around the periphery of the cytosolic face of the cell membrane, and the protein was found solely in the soluble fraction of cell extracts. Our hypothesis is that GlbN scavenges oxygen for and is a component of a membrane-associated microaerobically induced terminal cytochrome oxidase.
念珠藻UTEX 584的glbN基因与nifU和nifH相邻，它编码一种12 kDa的单体血红蛋白，该蛋白能以高亲和力结合氧气。在念珠藻UTEX 584中，当放氧速率被抑制到小于25 μmol O₂ mg叶绿素a⁻¹ h⁻¹时，固氮培养物的异形胞和营养细胞中GlbN的积累量均达到最大。GlbN的积累与NifH和铁氧还蛋白NADP⁺氧化还原酶（PetH或FNR）的最大合成量一致。对总共41株蓝细菌进行了筛选，包括40株固氮菌，代表蓝细菌所有五个分类中的16个属，以检测glbN或GlbN的存在。glbN以单拷贝形式存在于5株念珠藻菌株中。来自其他11株念珠藻和鱼腥藻菌株的基因组DNA，包括鱼腥藻PCC 7120菌株，与glbN探针没有杂交信号。在4株鱼腥藻和念珠藻菌株以及红海束毛藻中检测到一种组成型表达的18 kDa蛋白，它与GlbN抗体发生强烈交叉反应。对念珠藻MUN 8820菌株的nifU - nifH基因间区域进行了测序（1229 bp），与念珠藻UTEX 584中的等效区域约95%相同。这两个菌株nifU - nifH基因间区域的每条DNA链都有可能折叠成二级结构，其中超过50%的碱基内部配对。凝胶迁移实验证实，NtcA（BifA）结合了念珠藻UTEX 584的nifU - glbN基因间区域中位于glbN翻译起始位点上游约100个碱基处的一个位点。该位点与聚球藻PCC 7942菌株的glnA启动子区域有广泛的序列相似性。在体内，GlbN在细胞膜胞质面周边有特定且显著的亚细胞定位，并且该蛋白仅存在于细胞提取物的可溶部分。我们的假设是，GlbN为一种与膜相关的微需氧诱导型末端细胞色素氧化酶清除氧气并是其组成成分。
