Submitted to: BMC Structural Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2011
Publication Date: 3/2/2011
Citation: Yennamalli, R.M., Rader, A.J., Wolt, J.D., Sen, T.Z. 2011. Thermostability in endoglucanases is fold-specific. BMC Structural Biology. 11(10):1-15. Interpretive Summary: Thermostable proteins, specifically industrially important enzymes, are frequently studied in protein engineering studies. Understanding the thermostability helps in engineering to enhance protein activity thereby leading to a cost effective process. For biofuel production, enzymes currently used in biomass to bioethanol conversion are derived from microorganisms. Some of the limitations of the current technology are low yield and high cost of production of pre-processing enzymes, like endoglucanases. A more efficiently designed thermophilic endoglucanase to be inserted in maize will be very promising. However, thermophilic endoglucanases are poorly understood since previous studies to derive rules of thermophilicity focused on a large number of protein families, but not on particular folds of the same enzyme. In this study we have analyzed the available endoglucanase protein structures and have shown that protein folds rather than protein families are more important while defining rules for thermophilicity that will help scientists design more efficient enzymes for bioethanol production from maize, which will benefit the U.S. economy.
Technical Abstract: Endoglucanases are involved in the initial stages of cellulose breakdown, an essential step in the bioprocessing of lignocellulosic plant materials into bioethanol. Although these enzymes are economically important, we currently lack a basic understanding of how some endoglucanases can sustain their ability to function at elevated temperatures needed for bioprocessing, while others with the same fold cannot. In this study, we present a detailed comparative analysis of both thermophilic and mesophilic endoglucanases in order to gain insights into origins of thermophilicity. We used the Carbohydrate-Active enZymes (CAZy) database to build our endoglucanase protein datasets and analyzed their sequences and structures. Our results demonstrate that thermophilic endoglucanases and their mesophilic counterparts differ significantly in their amino acid compositions. Strikingly, these compositional differences are specific to protein folds and enzyme families, and lead to differences in intramolecular interactions in a fold-dependent fashion. However, when it comes to thermophilicity, there is a caveat of applying general heuristic rules based on averaged properties to specific proteins: although thermophilicity in endoglucanases is usually conferred through altering amino acid composition, in some cases even a single-point mutation is sufficient to convert a mesophilic protein into a thermophilic protein. Here, we provide fold-specific guidelines to control thermophilicity in endoglucanases that will make production of biofuels from plant biomass more efficient.