Biochemical Analysis Of A Novel Oxygen Sensor Protein In The N₂-Fixing Cyanobacterium Anabaena sp. PCC 7120

Abstract

An oxygen sensor may play an important role in the N₂-fixing cyanobacterium Anabaena sp. PCC 7120. FixL of rhizobia and DOS of Escherichia coli have a heme PAS domain as an oxygen sensor. We detected in the Anabaena genome a gene alr2428 that encodes a homologous heme PAS domain in addition to various signaling and DNA-binding domains. To analyze this heme PAS domain, we expressed this domain as a His-tagged protein. The purified protein was found to bind a heme. We prepared met, deoxy, O₂-binding and CO-binding forms and measured their absorption spectra and resonance raman spectra. The properties were very similar to those of DOS from E. coli, whose deoxy and met forms have hexacoordinate heme iron. However, no clear sixth ligand to iron was detected in Alr2428, when aligned with DOS from E. coli. Possible structure of the heme PAS domain in Alr2428 will be discussed.