Characterization of major lipid droplet proteins from Dunaliella

Many green algal species can accumulate large amounts of triacylglycerides (TAG) under nutrient deprivation, making them a potential source for production of biodiesel. TAG are organized in cytoplasmic lipid bodies, which contain a major lipid droplet protein termed MLDP. Green algae MLDP differ in sequence from plant oleosins and from animal perilipins, and their structure and function are not clear. In this study, we describe the isolation of MLDP from three species of the extreme halotolerant green algae Dunaliella. Sequence alignment with other green algae MLDP proteins identified a conserved 4-proline domain that may be considered as a signature domain of Volvocales green algae MLDP. Gold immunolabeling localized MLDP at the surface of lipid droplets in D. salina. The induction of MLDP by nitrogen deprivation is kinetically correlated with TAG accumulation, and inhibition of TAG biosynthesis impairs MLDP accumulation suggesting that MLDP induction is co-regulated with TAG accumulation. These results can lead to a better understanding of the structure and function of Volvocales green algae MLDP proteins.