Atomistic modeling of elasticity, plasticity and fracture of protein crystals
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0898-L10-03.1
Atomistic modeling of elasticity, plasticity and fracture of protein crystals Markus J. Buehler Massachusetts Institute of Technology, 77 Mass. Ave Room 1-272, Cambridge, MA 02139, USA, email: [email protected] ABSTRACT The structure and behavior of proteins plays an overarching role in determining their function in biological systems. In recent years, proteins have also been proposed as basis for new materials to be used in technological applications (Langer and Tirrell, Nature, 2004). It is known that protein crystals show very interesting mechanical behavior, as some of them are extremely fragile, while others can be quite sturdy. However, unlike other crystalline materials like silicon or copper, the mechanical properties of protein crystals have rarely been studied by atomistic computer modeling. As a first step towards more fundamental understanding of the mechanics of those materials, we report atomistic studies of mechanical properties of protein crystals using empirical potentials focusing on elasticity, plasticity and fracture behavior. Here we consider the mechanics of a small protein α-conotoxin PnIB from conus pennaceus. We use large-scale atomistic simulations to determine the low-strain elastic constants for different crystallographic orientations. We also study large-strain elastic properties including plastic deformation. Furthermore, we perform systematic studies of the effect of mutations on the elastic properties of the protein crystal. Our results indicate a strong impact of mutations on elastic properties, showing the potential of mutations to tailor mechanical properties. We conclude with a study of mode I fracture of protein crystals, relating our atomistic modeling results with Griffith’s theory of fracture. INTRODUCTION Biological materials may be essential to face critical challenges related to increased energy needs, needs for new medical applications, novel concepts in sensor and actuator design, reliability and robustness of devices, as well as conservation of resources and development of new structural materials. The combination of (i) high-level structural control of matter as achieved in nanoscience and nanotechnology, and (ii) integration of living/non-living systems Figure 1: Introduction and motivation. Our eventual objective is to developing understanding of the macroscopic properties of protein based materials ranging from the atomic scale. Proteins consist of different structural levels of detail, including the level of amino acid sequence (primary structure), arrangement of structural motifs, the overall folded three-dimensional geometry (tertiary structure), as well as the assembly of various proteins and/or substrate into agglomerates (quaternary structure).
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Figure 2: Subplot (a): The protein 1AKG as crystallized and deposited in the protein data bank by Hu and others in 1996 [1]. Subplot (b) shows two views defining the coordinate system used for our studies.
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