Degradation of polysaccharides by cellulases and xylanases plays an important role in the carbon cycle, but only occurs in plant cell walls, a few bacteria and some animals. This process is also critical in processes Such as biomass degradation and fuel production in the conversion cycles of cellulosic biomass. The enzyme CelM2 is bifunctional, because it is able to effectively hydrolyze barley glucan and xylan. Here, we show the crystal structure of the bifunctional enzyme CelM2, isolated from a metagenome library, and describe the sequence information and structure of its two domains. We believe that CelM2 is attractive as an industrial enzyme and that the structural results presented herein provide insights that are relevant to the genetic engineering of multifunctional enzymes. (C) 2009 Elsevier Inc. All rights reserved.