GlbN (cyanoglobin) is a peripheral membrane protein that is restricted to certain Nostoc spp

Abstract

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 mol of O 2 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.

Global Transcription Profiles of the Nitrogen Stress Response Resulting in Heterocyst or Hormogonium Development in Nostoc punctiforme

“…Different from Anabaena 7120 is the presence of glbN located between nifH and nifU. GlbN is a hemoglobin-like protein believed to be involved in oxygen scavenging for cytochrome oxidase and localizes specifically to heterocysts (34). Transcription of glbN follows the same pattern as the surrounding nif genes in N. punctiforme.…”

Nitrogen Control in Cyanobacteria

“…strain PCC 7120 (5). A gene designated glbN, which encodes a monomeric hemoglobin, has been found juxtaposed to nifU and nifH in Nostoc commune strain UTEX 584 (94) and is present in some other Nostoc strains as well (48).…”

Regulation of Cellular Differentiation in Filamentous Cyanobacteria in Free-Living and Plant-Associated Symbiotic Growth States

“…No plant-derived hemoglobin-like protein has been reported. Cyanoglobin, a heme protein with high affinity for oxygen, is found in many Nostoc strains, but some strains, including a few symbiotic strains, lack the protein (79). Free-living cyanobacteria can maintain high nitrogenase activities while growing under atmospheres ranging from 1 to 50% O 2 (131).…”