A unique, newly discovered four-member protein family involved in extracellular fatty acid binding in Yarrowia lipolytica

Background:
Yarrowia lipolytica, a nonconventional oleaginous yeast species, has attracted attention due to its high lipid degradation and accumulation capacities. Y. lipolytica is used as a chassis for the production of usual and unusual lipids and lipid derivatives. While the genes involved in the intracellular transport and activation of fatty acids in differ ent cellular compartments have been characterized, no genes involved in fatty acid transport from the extracellular medium into the cell have been identified thus far. In this study, we identified secreted proteins involved in extracel lular fatty acid binding.
Results:
Recent analysis of the Y. lipolytica secretome led to the identification of a multigene family that encodes four secreted proteins, preliminarily named UP1 to UP4. These proteins were efficiently overexpressed individually in wild-type and multideletant strain (Q4: Δup1Δup2Δup3Δup4) backgrounds. Phenotypic analysis demonstrated the involvement of these proteins in the binding of extracellular fatty acids. Additionally, gene deletion and overexpres sion prevented and promoted sensitivity to octanoic acid (C8) toxicity, respectively. The results suggested binding is dependent on aliphatic chain length and fatty acid concentration. 3D structure modeling supports the proteins’ role in fatty acid assimilation at the molecular level.
Conclusions:
We discovered a family of extracellular-fatty-acid-binding proteins in Y. lipolytica and have proposed to name its members eFbp1 to eFbp4. The exact mode of eFbps action remains to be deciphered individually and syner gistically; nevertheless, it is expected that the proteins will have applications in lipid biotechnology, such as improving fatty acid production and/or bioconversion.