XYLH encodes a xylose/H+ symporter from the highly related yeast species Debaryomyces fabryi and Debaryomyces hansenii

Abstract

The closely related yeasts Debaryomyces fabryi and Debaryomyces hansenii are excellent xylose consumers. We previously described the activity of a high-affinity xylose/H(+) symport from an industrial strain of D. hansenii subsequently reclassified as D. fabryi. We now report the identification of the gene encoding this permease, AY347871.2. This was retrieved from D. fabryi gDNA using a degenerate primer PCR strategy, based on conserved regions from the amino acid sequences of three well-characterized bacterial xylose/H(+) symporters. This sequence is 86% identical to another, DEHA2C11374p from D. hansenii type strain. DEHA2C11374p was conceptually ascribed to the major facilitator superfamily. The putative amino acid sequence of AY347871.2 and DEHA2C11374p presented a hydrophobicity pattern compatible with plasma membrane proteins. The last was functionally expressed in Saccharomyces cerevisiae. The sensitivity of transport activity to a protonophore confirmed its dependence on proton motive force, as expected from a symporter. We named D. fabryi AY347871.2 and D. hansenii DEHA2C11374p as XYLH from Xylose/H(+) symport. Based on the very high similarity, we suggested that Scheffersomyces stipitis Xut3 and Aspergillus nidulans AN8400.2 may also encode xylose high-affinity permeases.