Protein secretion in wild-type and Othac1 mutant strains of thermotolerant methylotrophic yeast Ogataea thermomethanolica TBRC656.

In yeasts, Hac1 transcription factor of the unfolded protein response (UPR) regulates many genes involved in secretory pathways. The thermotolerant methylotrophic yeast Ogataea thermomethanolica TBRC656 is a host for heterologous protein secretion. To understand the role of OtHac1 on the secretome of O. thermomethanolica, a comparative proteomic analysis using LC-MS/MS was employed to identify proteins with altered secretion levels when OtHac1 was mutated. 268 proteins were detected in the extracellular medium of O. thermomethanolica wild-type control and Othac1 mutant strains. A number of metabolic enzymes functioning in amino acid, carbohydrate, glycan, and lipid metabolism showed altered secretion in the mutant suggesting that OtHac1 may play a role in mediating extracellular metabolism. Most of the extracellular proteins identified do not contain canonical signal sequences suggesting that they are secreted via unconventional protein secretion pathways. Collectively, the data provide insights into protein secretion and OtHac1 function in O. thermomethanolica which will be useful for developing efficient host for protein production.