QUANTUM CRYSTALLOGRAPHY OF BIOLOGICAL MOLECULES--INSULIN AND ITS FRAGMENTS

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The broad, long term objectives of this research are to develop the next generation of crystallography, viz., one founded directly upon quantum mechanics, and applicable to proteins and DNA. Our specific aim is the quantum crystallography of the biologically important protein insulin. The impact of this, includes having for the first time the quantum geometrical and electronic structure of the insulin molecule, but also a methodology that will be generally applicable to proteins and DNA, and the drug molecules with which they interact. Such information impacts directly upon health implications of biochemistry through applications, which follow upon knowledge of molecular structure & function. Quantum Crystallography delivers both geometrical structure, the determining factor which underlies the possibility of :lock & key" molecular interactions, and electronic structure which determines the strength and mechanisms of such interactions. The importance of this for rational drug design would be enormous. Our research design is based upon the quantum mechanical realization that atomic orbital overlap decreases rapidly with interatomic distance. This "near-sightedness" of orbitals leads to a description of a whole biological molecule in terms of the sum of its parts, called kernels. The quantum description requires only the kernels and a few atoms in their neighborhood altogether called fragments. Thus, quantum mechanics of giant molecules, e.g., proteins and DNA, is rigorously reduced to knowledge of their fragments, vastly simplifying both experimental and theoretical components of their crystal structure. The fragment concept applies equally to the crystallographic X-ray refinement of structure and its ab initio calculation from the Schrodinger equation. Comparison of the two cases ensures accuracy of results. In either cases the time involved increases essentially linearly with complexity, thus making the quantum properties of biological molecules practicably attainable.