Identification and characterization of a gene conferring stress resistance in Escherichia coli and cyanobacteria.

Picosynechococcus sp. strain NKBG15041c is a cyanobacterium isolated from the ocean and while it is known for rapid growth, the basis of its high proliferation capacity remains unclear. Screening for genes which may underlie this rapid growth using E. coli, we identified a gene that promotes growth and enhances stress resistance. The protein encoded by this gene (PcSyn14890) is specific to cyanobacteria, and no homologs with known functions have been identified. In P. NKBG15041c, expression of this gene was induced during the early stage of growth and when introduced into a different cyanobacterium, the transformants exhibited accelerated growth, enhanced stress resistance, and increased ATP and Chlorophyll a content. We hypothesized that PcSyn14890 functions as an ATP-independent chaperone. To investigate further, recombinant PcSyn14890 was expressed in E. coli, purified, and subjected to structural and functional characterization. PcSyn14890 existed as monomers or dimers and did not form higher-order oligomers. Its small-angle X-ray scattering profile was consistent with the AlphaFold3 predicted structure, and the CD spectrum confirmed its β-sheet-rich composition. However, contrary to expectations, PcSyn14890 was unable to prevent the thermal aggregation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Thus, we conclude that PcSyn14890 does not function as a general molecular chaperone and therefore the mechanism by which expression of PcSyn14890 enhances the stress tolerance of E. coli and S. PCC6803 requires further investigation.