Cellular and functional specificity among ferritin‐like proteins in the multicellular cyanobacterium N ostoc punctiforme

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Summary: Ferritin‐like proteins constitute a remarkably heterogeneous protein family, including ferritins, bacterioferritins and D ps proteins. The genome of the filamentous heterocyst‐forming cyanobacterium N ostoc punctiforme encodes five ferritin‐like proteins. In the present paper, we report a multidimensional characterization of these proteins. Our phylogenetic and bioinformatics analyses suggest both structural and physiological differences among the ferritin‐like proteins. The expression of these five genes responded differently to hydrogen peroxide treatment, with a significantly higher rise in transcript level for N pun_ F 3730 as compared with the other four genes. A specific role for N pun_ F 3730 in the cells tolerance against hydrogen peroxide was also supported by the inactivation of N pun_ F 3730 , N pun_ R 5701 and N pun_ R 6212 ; among these, only the Δ N pun_ F 3730 strain showed an increased sensitivity to hydrogen peroxide compared with wild type. Analysis of promoter‐ GFP reporter fusions of the ferritin‐like genes indicated that N pun_ F 3730 and N pun_ R 5701 were expressed in all cell types of a diazotrophic culture, while N pun_ F 6212 was expressed specifically in heterocysts. Our study provides the first comprehensive analysis combining functional differentiation and cellular specificity within this important group of proteins in a multicellular cyanobacterium.

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