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Functional expression of the lactate permease Jen1p of Saccharomyces cerevisiae in Pichia pastoris.

ABSTRACT: In Saccharomyces cerevisiae the activity for the lactate-proton symporter is dependent on JEN1 gene expression. Pichia pastoris was transformed with an integrative plasmid containing the JEN1 gene. After 24 h of methanol induction, Northern and Western blotting analyses indicated the expression of JEN1 in the transformants. Lactate permease activity was obtained in P. pastoris cells with a V (max) of 2.1 nmol x s(-1) x mg of dry weight(-1). Reconstitution of the lactate permease activity was achieved by fusing plasma membranes of P. pastoris methanol-induced cells with Escherichia coli liposomes containing cytochrome c oxidase, as proton-motive force. These assays in reconstituted heterologous P. pastoris membrane vesicles demonstrate that S. cerevisiae Jen1p is a functional lactate transporter. Moreover, a S. cerevisiae strain deleted in the JEN1 gene was transformed with a centromeric plasmid containing JEN1 under the control of the glyceraldehyde-3-phosphate dehydrogenase constitutive promotor. Constitutive JEN1 expression and lactic acid uptake were observed in cells grown on either glucose and/or acetic acid. The highest V (max) (0.84 nmol x s(-1) x mg of dry weight(-1)) was obtained in acetic acid-grown cells. Thus overexpression of the S. cerevisiae JEN1 gene in both S. cerevisiae and P. pastoris cells resulted in increased activity of lactate transport when compared with the data previously reported in lactic acid-grown cells of native S. cerevisiae strains. Jen1p is the only S. cerevisiae secondary porter characterized so far by heterologous expression in P. pastoris at both the cell and the membrane-vesicle levels.

SUBMITTER: Soares-Silva I

PROVIDER: S-EPMC1223809 | biostudies-other | 2003 Dec

REPOSITORIES: biostudies-other

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Project description:Basidiomycete high-redox potential laccases (HRPLs) working in human physiological fluids (pH 7.4, 150 mM NaCl) arise great interest in the engineering of 3D-nanobiodevices for biomedical uses. In two previous reports, we described the directed evolution of a HRPL from basidiomycete PM1 strain CECT 2971: i) to be expressed in an active, soluble and stable form in Saccharomyces cerevisiae, and ii) to be active in human blood. In spite of the fact that S. cerevisiae is suited for the directed evolution of HRPLs, the secretion levels obtained in this host are not high enough for further research and exploitation. Thus, the search for an alternative host to over-express the evolved laccases is mandatory.A blood-active laccase (ChU-B mutant) fused to the native/evolved ?-factor prepro-leader was cloned under the control of two different promoters (P(AOX1) and P(GAP)) and expressed in Pichia pastoris. The most active construct, which contained the P(AOX1) and the evolved prepro-leader, was fermented in a 42-L fed-batch bioreactor yielding production levels of 43 mg/L. The recombinant laccase was purified to homogeneity and thoroughly characterized. As happened in S. cerevisiae, the laccase produced by P. pastoris presented an extra N-terminal extension (ETEAEF) generated by an alternative processing of the ?-factor pro-leader at the Golgi compartment. The laccase mutant secreted by P. pastoris showed the same improved properties acquired after several cycles of directed evolution in S. cerevisiae for blood-tolerance: a characteristic pH-activity profile shifted to the neutral-basic range and a greatly increased resistance against inhibition by halides. Slight biochemical differences between both expression systems were found in glycosylation, thermostability and turnover numbers.The tandem-yeast system based on S. cerevisiae to perform directed evolution and P. pastoris to over-express the evolved laccases constitutes a promising approach for the in vitro evolution and production of these enzymes towards different biocatalytic and bioelectrochemical applications.

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Functional expression of the lactate permease Jen1p of Saccharomyces cerevisiae in Pichia pastoris.

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