Isolation of a Novel Oil Globule Protein from the Green Alga Haematococcus pluvialis (Chlorophyceae)

Abstract

Cytoplasmic oil globules of Haematococcus pluvialis (Chlorophyceae) were isolated and analyzed for pigments, lipids and proteins. Astaxanthin appeared to be the only pigment deposited in the globules. Triacyglycerols were the main lipids (more than 90% of total fatty acids) in both the cell-free extract and in the oil globules. Lipid profile analysis of the oil globules showed that relative to the cell-free extract, they were enriched with extraplastidial lipids. A fatty acids profile revealed that the major fatty acids in the isolated globules were oleic acid (18:1) and linoleic acid (18:2). Protein extracts from the globules revealed seven enriched protein bands, all of which were possible globule-associated proteins. A major 33-kDa globule protein was partially sequenced by MS/MS analysis, and degenerate DNA primers were prepared and utilized to clone its encoding gene from cDNA extracted from cells grown in a nitrogen depleted medium under high light. The sequence of this 275-amino acid protein, termed the Haematococcus Oil Globule Protein (HOGP), revealed partial homology with a Chlamydomonas reinhardtii oil globule protein and with undefined proteins from other green algae. The HOGP transcript was barely detectable in vegetative cells, but its level increased by more than 100 fold within 12 h of exposure to nitrogen depletion/high light conditions, which induced oil accumulation. HOGP is the first oil-globule-associated protein to be identified in H. pluvialis, and it is a member of a novel gene family that may be unique to green microalgae.

A Lipid Droplet Protein of Nannochloropsis with Functions Partially Analogous to Plant Oleosins

“…The purified LD fractions from N-deprived Nannochloropsis cells were highly enriched in TAG and showed an accumulation of carotenoids and depletion of chlorophyll as is typical for LDs of other algae (Moellering and Benning, 2010;Peled et al, 2011;Fig. 1A).…”

“…Orthologs of the major LD protein are present in other green algae (Peled et al, 2011). A wide variety of parameters affects the abundance of LDs in Chlamydomonas , and there is ample evidence that turnover of LDs plays crucial roles in cellular lipid or carbon homeostasis.…”

Bioinformatics Reveal Five Lineages of Oleosins and the Mechanism of Lineage Evolution Related to Structure/Function from Green Algae to Seed Plants

“…In the primitive green alga C. reinhardtii, LDs in situ are small and probably have less than 1% of the surface covered with oleosin or an oleosin-like protein (Huang et al, 2013b). Thus, these LDs in the cytosol would be stabilized by other molecules, most likely storage lipidmetabolizing enzymes, as is the case with yeast LDs, and/or by association with the ER or cytoskeleton or other potential structural proteins (Moellering and Benning, 2010;Peled et al, 2011;Davidi et al, 2012;Vieler et al, 2012).…”

Major Lipid Body Protein: A Conserved Structural Component of Lipid Body Accumulated during Abiotic Stress in S. quadricauda CASA-CC202

“…MLDP has been reported in green algal lineages, such as Chlorella vulgaris, Volvox carteri, Dunaliella salina, and Haematococcus pluvialis, however not mapped in diatoms, red algae, or seed plants for which sequenced genomes are available (Moellering and Benning, 2010;Peled et al, 2011;Davidi et al, 2012). D. salina MLDP shares high homology with conserved proline-rich domain in C-terminal end of green algal linage.…”