Biomacromolecular assemblies

Self-sorting is one of the most fundamental processes in living systems, which led complex mixtures of biomolecules (e.g., proteins, nucleic acids, oligosaccharides, lipids) to self-organize into larger biomacromolecular assemblies (e.g., DNA double-helix, multienzyme complexes, ribosomes) and finally into cellular compartments essential for the development of life on Earth. 

Experimental dipole moments may be used to check the validity of electrostatic calculations. In the past, dipole moments of proteins were often characterized by measurements of dielectric relaxation. More information may be obtained by measurements of the electric dichroism because these measurements provide not only the magnitude of the dipole moment but also the optical anisotropy with respect to the dipole vector. Thus, measurements of the electric dichroism provide a more rigorous test for calculations of electrostatic parameters of proteins. Using the calculations described earlier for pK s of titratable groups, one can predict dipole moments of proteins and their axes given by the principal axes of the rotational diffusion tensor and compare them with electrooptical data. ° One important aspect of comparison of computed and experimental dipole moment is that computations of dipole moments, optical anisotropy, and rotational diffusion coefficients can be used in combination with experimental electrooptical procedures to determine the long-range structure of biomacromolecular assemblies, such as the complexes of DNA and proteins described by Pbrschke et al. so... 

There is considerable interest in the coordination" and catalytic chemistries of these discrete clusters. Because of its high electron count, the hexaaquo ion [Ta6(p-Br)i2(OH2)6] has been used frequently for phase determination of isomorphous protein derivatives by SIR, MIR, SIRAS/MIRAS, and SAD/MAD methods in biomacromolecular crystallography. This use is growing as larger biomacromolecular structures and assemblies (e.g., membrane proteins, ribosomes, proteasomes) are studied. 

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