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Molecular Analysis of Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae Reveals a Determinant Role for the AGT1 Permease

Sergio L. Alves Jr.,^1,2 Ricardo A. Herberts,^1,3 Claudia Hollatz,^1,3 Debora Trichez,^1,3 Luiz C. Miletti,^1, Pedro S. de Araujo,⁴ and Boris U. Stambuk^1,3*

Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, SC 88040-900, Brazil,¹ Programa de Pós-graduação Interunidades em Biotecnologia, USP-IPT-I BUTANTAN, São Paulo, Brazil,² Programa de Pós-graduação em Biotecnologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, Brazil,³ Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil⁴

Received 14 November 2007/ Accepted 6 January 2008

Incomplete and/or sluggish maltotriose fermentation causes both quality and economic problems in the ale-brewing industry. Although it has been proposed previously that the sugar uptake must be responsible for these undesirable phenotypes, there have been conflicting reports on whether all the known -glucoside transporters in Saccharomyces cerevisiae (MALx1, AGT1, and MPH2 and MPH3 transporters) allow efficient maltotriose utilization by yeast cells. We characterized the kinetics of yeast cell growth, sugar consumption, and ethanol production during maltose or maltotriose utilization by several S. cerevisiae yeast strains (both MAL constitutive and MAL inducible) and by their isogenic counterparts with specific deletions of the AGT1 gene. Our results clearly showed that yeast strains carrying functional permeases encoded by the MAL21, MAL31, and/or MAL41 gene in their plasma membranes were unable to utilize maltotriose. While both high- and low-affinity transport activities were responsible for maltose uptake from the medium, in the case of maltotriose, the only low-affinity (K_m, 36 ± 2 mM) transport activity was mediated by the AGT1 permease. In conclusion, the AGT1 transporter is required for efficient maltotriose fermentation by S. cerevisiae yeasts, highlighting the importance of this permease for breeding and/or selection programs aimed at improving sluggish maltotriose fermentations.

Published ahead of print on 18 January 2008.

Present address: Departamento de Produção Animal e Alimentos, Centro de Ciências Agroveterinárias, Universidade do Estado de Santa Catarina, Lages, Brazil.