The present invention provides for heterologous expression of polypeptides encoded by wild-type and codon-optimized cbh2 genes from the organisms Cochliobolus heterostrophus, Gibberella zeae, Irpex lacteus, Volvariella volvacea, and Piromyces sp. in host cells, such as the yeast Saccharomyces cerevisiae. The expression in such host cells of the corresponding genes, and variants and combinations thereof, result in improved specific activity of the expressed cellobiohydrolases. Thus, such genes and expression systems are useful for efficient and cost-effective consolidated bioprocessing systems.