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Protein Design

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Proteins play major mechanical roles in a cell. Mechanical properties of proteins can be substantially modulated by slight changes in their amino acid composition, an ability essential to bacterial cells, which use protein repeats with small modifications to tune their mechanical strength, and thus their functional properties. A prime example of the role of biomechanics in the cell is found in symbiont gut bacteria who need to hold to their food source in such turbulent environments as the rumen of the cow. Proteins evolved for this purpose are known actually to be among the strongest mechanical biomolecules. Key to the process are molecular tentacles, so-called cellulosomes, on the surface of symbiotic bacteria. The cellulosomes develop a tight grasp on and then effective cleavage of hardy cellulose fibers of the grass. In a joint experimental-computational study researchers investigated the mechanical properties of cohesin, a major cellulosome component, under force. Using NAMD, all-atom steered molecular dynamics (SMD) simulations on homology models offered insight into the process of cohesin unfolding under force. Based on the differences among the individual force propagation pathways and their associated correlation communities, the researchers were capable of designing protein mutants to tune the mechanical stability of the weakest cohesin. The proposed mutants were tested with high-throughput atomic force microscopy experiment revealing that in one case a single alanine to glycine point mutation suffices to more than double the mechanical stability. Read more about our cellulosome research here.