Mapping the Membrane Proteome of Anaerobic Gut Fungi using RNA-Seq

Abstract

Anaerobic gut fungi reside in the digestive tract of large herbivores where they enable the digestion of resilient plant biomass into fermentable sugars. It is likely that the membrane envelope of these important but woefully understudied organisms is involved in their cellulolytic lifestyle. Our studies suggest that these fungal membranes contain a number of sugar transporters and sensors that are potentially valuable tools for the biotech community. Characterization of these entities will also shed light on the remarkable abilities of these most early diverging eukaryotes. Here, we have used RNA-Seq to study the membrane transcriptome of three strains of gut fungi: Anaeromyces sp. S4, Piromyces sp. finn, and Neocallimastix sp. G1 at high resolution. Hydropathy analyses suggest that at least 20% of the transcripts in each strain encode proteins that are integral membrane proteins. Among these are transporters and proteins involved in energy metabolism and signaling. Surprisingly, we find a number of membrane-anchored proteins that are homologous to bacterial sugar-binding proteins. Some of these putative sugar-binding domains are fused to class 3 G-protein coupled receptors (GPCRs), and as such suggest that GPCRs play a sugar-sensing role in primitive fungi.