Quantitative Overview of N₂ Fixation in Nostoc punctiforme ATCC 29133 through Cellular Enrichments and iTRAQ Shotgun Proteomics

Abstract

Nostoc punctiforme ATCC 29133 is a photoautotrophic cyanobacterium with the capacity to fix atmospheric N 2. Its ability to mediate this process is similar to that described for Nostoc sp. PCC 7120, where vegetative cells differentiate into heterocysts. Quantitative proteomic investigations at both the filament level and the heterocyst level are presented using isobaric tagging technology (iTRAQ), with 721 proteins at the 95% confidence interval quantified across both studies. Observations from both experiments yielded findings confirmatory of both transcriptional studies, and published Nostoc sp. PCC 7120 iTRAQ data. N. punctiforme exhibits similar metabolic trends, though changes in a number of metabolic pathways are less pronounced than in Nostoc sp. PCC 7120. Results also suggest a number of proteins that may benefit from future investigations. These include ATP dependent Zn-proteases, N-reserve degraders and also redox balance proteins. Complementary proteomic data sets from both organisms present key precursor knowledge that is important for future cyanobacterial biohydrogen research.

Transformation of Thylakoid Membranes during Differentiation from Vegetative Cell into Heterocyst Visualized by Microscopic Spectral Imaging

“…Because of the decrease in PSII and PBS in heterocysts, the relative abundance of PSI should inevitably increase. This prediction was confirmed by a recent mass spectrometrybased proteomic study on filaments of A. variabilis (Ow et al, 2009). In that study, the relative abundance of PSI was 3.3-fold higher on average in heterocyst cells than in vegetative cells.…”

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

“…PCC 7120 (162) in non-Fe-limited cultures may indicate that other, still unresolved electron transfer pathways operate in these specialized cells. Similar evidence may be derived from work with Nostoc punctiforme ATCC 29133, where two ferredoxin-like electron transport proteins show a markedly increased abundance together with FNR in heterocysts (163). Flavodoxin was reported to enhance cyclic electron flow around photosystem I in salt-stressed cells (89), which may also occur in N 2 -fixing heterocysts.…”

“…Glucose residues from glycogen are utilized via the oxidative pentose phosphate pathway, finally resulting in pyruvate (208). Its further degradation is hampered by the fact that the tricarboxylic acid cycle is incomplete in cyanobacteria because neither an oxoglutarate dehydrogenase complex nor an oxoglutarate:ferredoxin oxidoreductase is present (208), which has been confirmed by recent large-scale proteomic studies (162,163). This prevents the complete degradation of the C2 moiety to CO 2 and NAD(P)H. Cyanobacteria apparently prefer to utilize NADP ϩ rather than NAD ϩ in catabolism (51), since several enzymes, such as isocitrate dehydrogenase (165) and glyceraldehyde-3-phosphate-dehydrogenase (166), are NADP ϩ rather than NAD ϩ dependent.…”

“…Another ferredoxin-like protein, FdxB (PatB), is specifically expressed in heterocysts (107). Neither ferredoxin was identified in a quantitative proteomic investigation of heterocysts (163).…”

Current trends in high throughput proteomics in cyanobacteria

“…Results of this nature can also be integrated with other systems-biology approaches, such as other complementary layers of metabolic data, DNA microarrays, metabolite targets, or more generally flux data [74,75]. Likewise, global proteomics changes related to cellular differentiation have only been scarcely studied [58,59]. Other potential investigations, such as the proteomic changes in hormogonia, remain to be carried out [76].…”