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Title: A rigid network of long-range contacts increases thermostability in a mutant endoglucanase

item RADER, ANDREW - Indiana University-Purdue University
item YENNAMALLI, RAGOTHAMAN - Iowa State University
item HARTER, ANDREW - Indiana University-Purdue University
item Sen, Taner

Submitted to: Journal of Biomolecular Structure and Dynamics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2012
Publication Date: 7/3/2012
Citation: Rader, A.J., Yennamalli, R.M., Harter, A.K., Sen, T.Z. 2012. A rigid network of long-range contacts increases thermostability in a mutant endoglucanase. Journal of Biomolecular Structure and Dynamics. DOI:10.1080/07391102.2012.689696.

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. In this work, we look at a very special case of an endoglucanase protein, where a single mutation converts this mesophile into a thermophile. What caused this change defies current theories. We explain this change by arguing that allosteric properties of proteins using rigidity network are responsible in creating the thermophilicity trait. This new understanding can help scientists to design more efficient enzymes for bioethanol production of maize.

Technical Abstract: Thermodynamic stability of a protein, at elevated temperatures, is a key factor for thermophilic enzymes to catalyze their specific reactions. Our understanding of biological determinants of thermophilicity, however, is far from complete. Different groups suggested different atomistic factors that cause proteins to preserve their activity at high temperatures. Among them are specific local interatomic interactions or enrichment of specific amino acid types. The case of glycosyl hydrolase family endoglucanase of T. reesei defies all the current hypotheses for thermophilicity: only one mutation far from the active site, A35V, converts this mesophilic protein into a thermophile without significant change in the protein structure. This substantial change in enzymatic activity cannot be explained on the basis of intramolecular interactions alone. Here we present a more global view of the thermophilicity and argue that the A35V mutational change affects the rigidity network of the whole protein via long range/non-local interactions and this allosteric effect metamorphoses a mesophilic protein into a thermophile.