Analysis of secretome and N-glycosylation of Chlorella species

Chlorella, unicellular green algae, has been spotlighted not only as a model organism but also as a cell factory for various metabolites, biofuels and biopharmaceuticals. In order to accelerate the use Chlorella as a future biopharmaceutical platform, secretomes and the N-glycosylation of the secreted proteins were analyzed from Chlorella vulgaris UTEX395 and an arctic Chlorella species ArM0029B. From liquid chromatography-tandem mass spectrometry analysis, 428 and 56 extracellular proteins from the culture of UTEX395 and ArM0029B, respectively, were analyzed. Most of the secretomes are related to metabolic processes including enzymes of carbonic anhydrases, chitinases, phosphatases and oxidases. Some of secretomes are related to extracellular fatty acid metabolic process and cell wall proteins giving clues for unknown Chlorella cell wall structure. Both N-glycans of the secreted proteins showed methylated oligomannosidic structure, but ArM0029B N-glycans showed pauci mannose with pentose and methylation. In silico analysis based on the N-glycan structures provided putative N-glycosylation pathways in both strains. We believe that the findings in this study extend our knowledge of Chlorella and evolutionary process of land plants. Moreover, it would contribute to the development of biotechnological application of Chlorella.