title: The effect of specific growth rate on protein synthesis and secretion in the filamentous fungus Trichoderma reesei.
abstract: Trichoderma reesei was cultivated in chemostat cultures on lactose-containing medium. The cultures were characterized for growth, consumption of the carbon source and protein production. Secreted proteins were produced most efficiently at low specific growth rates, 0.022-0.033 h(-1), the highest specific rate of total protein production being 4.1 mg g(-1) h(-1) at the specific growth rate 0.031 h(-1). At low specific growth rates, up to 29 % of the proteins produced were extracellular, in comparison to only 6-8 % at high specific growth rates, 0.045-0.066 h(-1). To analyse protein synthesis and secretion in more detail, metabolic labelling of proteins was applied to analyse production of the major secreted protein, cellobiohydrolase I (CBHI, Cel7A). Intracellular and extracellular labelled CBHI was quantified and analysed for pI isoforms in two-dimensional gels, and the synthesis and secretion rates of the molecule were determined. Both the specific rates of CBHI synthesis and secretion were highest at low specific growth rates, the optimum being at 0.031 h(-1). However, at low specific growth rates the secretion rate/synthesis rate ratio was significantly lower than that at high specific growth rates, indicating that at low growth rates the capacity of cells to transport the protein becomes limiting. In accordance with the high level of protein production and limitation in the secretory capacity, the transcript levels of the unfolded protein response (UPR) target genes pdi1 and bip1 as well as the gene encoding the UPR transcription factor hac1 were induced.
authors.affiliation: VTT Biotechnology, PO Box 1500 (Tietotie 2, Espoo), FIN-02044 VTT, Finland.
authors.forename: Tiina M
authors.initials: TM
authors.lastname: Pakula
authors.affiliation: VTT Biotechnology, PO Box 1500 (Tietotie 2, Espoo), FIN-02044 VTT, Finland.
authors.forename: Katri
authors.initials: K
authors.lastname: Salonen
authors.affiliation: VTT Biotechnology, PO Box 1500 (Tietotie 2, Espoo), FIN-02044 VTT, Finland.
authors.forename: Jaana
authors.initials: J
authors.lastname: Uusitalo
authors.affiliation: VTT Biotechnology, PO Box 1500 (Tietotie 2, Espoo), FIN-02044 VTT, Finland.
authors.forename: Merja
authors.initials: M
authors.lastname: Penttilä
mesh_terms: D001692:Biological Transport; D002480:Cellulase / Q000378:metabolism; D043366:Cellulose 1,4-beta-Cellobiosidase / Q000378:metabolism; D003470:Culture Media; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D007785:Lactose / Q000378:metabolism*; D017510:Protein Folding; D012269:Ribosomal Proteins / Q000378:metabolism; D014242:Trichoderma / Q000254:growth & development* / Q000378:metabolism
chemical_list: D003470:Culture Media; D005656:Fungal Proteins; D012269:Ribosomal Proteins; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase; D007785:Lactose