Philosophical Society of Washington

The 68th Joseph Henry Lecture:

Quantum Crystallography, a Tool for Enhancing Information from Crystallographic Data

Jerome Karle
Naval Research Laboratory

– and –

Visualization of an Ion Channel by use of Crystallography

Isabella Karle
Naval Research Laboratory


2106th Meeting Abstract
Friday, May 07, 1999 at 8:30 PM

Abstract:

Quantum Crystallography, a Tool for Enhancing Information from Crystallographic Data: Quantum Crystallography is a developing area of research that makes use of crystallographic in with the techniques of quantum mechanics. Crystallographic information facilitates quantum mechanicalformation in combination with the techniques of quantum mechanics. Crystallographic information facilitates quantum mechanical calculations and is generally indispensable for the calculations to proceed. This arises because the geometry of molecules can readily change in the crystalline state and it is also necessary to know how the molecules pack in order to make meaningful calculations. On the other hand, the use of the theoretical methods of quantum mechanics can greatly extend the information available from a crystallographic experiment. This can concern, for example, a determination of charge distributions, a variety of energies, and electron densities. Applications to be discussed include an energetic molecule, 1,1-diamino-dinitroethylene and the polypeptide antibiotic, zervamicin. This is an opportune time for developing quantum crystallography because the recent major advances in parallel computing and the computer programs for handling the very large problems that arise assure that good progress is in the offing.

Visualization of an Ion Channel by use of Crystallography: A family of peptaibols found in spores in the soil perform antibiotic functions by transporting potassium ions through cell membranes. Single crystals have been prepared of two members of this family, the 16-residue peptides zervamicin and antiamoebin, and their structures established to a high resolution by X-ray diffraction analyses. Aspects of the structures to be discussed are the nature of the severely bent helices assumed by the peptides, the assembly of several helical peptimolecules that form the ion channel, the environment of the ion channel in a surround of long chain alcohol veral helical peptide molecules that form the ion channel, the environment of the ion channel in a surround of long chain alcohol molecules that mimic membrane material, and the gating mechanism that regulates the passage of one potassium ion per opening of the gate.

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