Proteome-wide analysis and diel proteomic profiling in the cyanobacterium Arthrospira platensis PCC 8005

The filamentous cyanobacteriumArthrospira platensishas a long history of use as a food supply and it has been used by the European Space Agency in the MELiSSA project, an artificial microecosystem which supports life during long-term manned space missions. This study assesses progress in the field of cyanobacterial shotgun proteomics and light/dark diurnal cycles by focusing onArthrospira platensis. Several fractionation workflows including gel-free and gel-based protein/peptide fractionation procedures were used and combined with LC-MS/MS analysis, enabling the overall identification of 1306 proteins, which represents 21% coverage of the theoretical proteome. A total of 30 proteins were found to be significantly differentially regulated under light/dark growth transition. Interestingly, most of the proteins showing differential abundance were related to photosynthesis, the Calvin cycle and translation processes. A novel aspect and major achievement of this work is the successful improvement of the cyanobacterial proteome coverage using a 3D LC-MS/MS approach, based on an immobilized metal affinity chromatography, a suitable tool that enabled us to eliminate the most abundant protein, the allophycocyanin. We also demonstrated that cell growth follows a light/dark cycle inA. platensis. This preliminary proteomic study has highlighted new characteristics of theArthrospira platensisproteome in terms of diurnal regulation

Cartoon depicting proteins associated with photosynthesis that are differentially regulated under the LD cycle.

<p>Each protein of the diagram is colored based on increased (red) or decreased abundance (blue) relative to the dark growth phase. Proteins colored in grey were not quantified.</p

Figure 2

<p>IMAC-Copper chromatogram (A). 4-20% SDS PAGE (B). Venn diagram showing non-redundant proteins between the two fractions (C). The twenty highest emPAI values in both the flowthrough (inner circle) and elution (outer circle) fractions (D). Histogram representing the emPAI values of the 6 most abundant proteins found to be common between the flowthrough and eluate (E).</p

Distribution of the fold-changes of all proteins quantified (185) in both biological replicates of the LD growth cycle using the post-digest ICPL method.

<p>Distribution of the fold-changes of all proteins quantified (185) in both biological replicates of the LD growth cycle using the post-digest ICPL method.</p

Venn diagram showing non-redundant proteins identified using: IEF, SDS-PAGE, 2D-LC, and 3D-LC MS/MS (IMAC-Cu²⁺).

<p>Venn diagram showing non-redundant proteins identified using: IEF, SDS-PAGE, 2D-LC, and 3D-LC MS/MS (IMAC-Cu²⁺).</p

Growth curve of <i>A</i>. <i>platensis</i> under a 12-hour LD cycle.

<p>Growth curve of <i>A</i>. <i>platensis</i> under a 12-hour LD cycle.</p