Noncovalent supramolecular complexes

Finally, to produce the structural and functional devices of the cell, polypeptides are synthesized by ribosomal translation of the mRNA. The supramolecular complex of the E. coli ribosome consists of 52 protein and three RNA molecules. The power of programmed molecular recognition is impressively demonstrated by the fact that aU of the individual 55 ribosomal building blocks spontaneously assemble to form the functional supramolecular complex by means of noncovalent interactions. The ribosome contains two subunits, the 308 subunit, with a molecular weight of about 930 kDa, and the 1590-kDa 50S subunit, forming particles of about 25-nm diameter. The resolution of the well-defined three-dimensional structure of the ribosome and the exact topographical constitution of its components are still under active investigation. Nevertheless, the localization of the multiple enzymatic domains, e.g., the peptidyl transferase, are well known, and thus the fundamental functions of the entire supramolecular machine is understood [24]. 

Here, the concept of linkage implies only that each intermolecular noncovalent bond is sufficiently large compared with kTto withstand ambient thermal collisions. Thus, for near-standard-state conditions (where kT 0.6kcal mol-1), even weak noncovalent interactions of 1-2 kcal mol-1 may be adequate to yield supramolecular complexes with stable equilibrium populations, thereby becoming true constituent units of the phase of lowest free energy. 

Supramolecular complexes are held together by noncovalent interactions and form a hierarchy of structures, some visible with the light microscope. When individual molecules are removed from these complexes to be studied... 

Once in its native conformation, a protein may associate noncovalently with other proteins, or with nucleic acids or lipids, to form supramolecular complexes such as chromosomes, ribosomes, and membranes. The individual molecules of these complexes have specific, high-affinity binding sites for each other, and within the cell they spontaneously form functional complexes. 

Molecules incorporating interlocked [refs. 6, 7] components (Fig. 10.1) and their supramolecular analogs are suitable candidates for the generation of bistable chemical systems. A [2]pseudorotaxane is a supramolecular complex composed of a macrocyclic host encircling a linear guest. The two components are held together solely by noncovalent bonding interactions and they can... 

Over the past decade, ESI-MS has been successfully used to study and characterize supramolecular complexes,56 58 after the detection of noncovalent receptor-ligand complexes by ESI-MS was first reported by Ganem et al. in 1991.59 A number of methods have been reported in the recent literature for the quantitative determination of noncovalent binding interactions using soft ionization mass spectrometry.60,61 However, to the best of our knowledge, supramolecular interactions have not yet been studied in a microreactor interfaced to a mass spectrometer. 

As to noncovalent interactions, the picture is less clear. Based on a limited number of experimental data regarding H-bonded supramolecular complexes. Hunter and coworkers obtained a relationship for short chains between the EM and the number of single bonds in the connecting chain d ... 

The values of EM are in the complete data set range from 10 —10 M (Fig. 8A). The EM values for the DMC data set have a somewhat narrower range than for the other data set, but both distributions have a clear maximum at an EM value of approximately 100 mM. More than 50% of the systems in both data sets have EM values between 10 mM and 1 M. The distribution of EM values obtained for noncovalent interactions in supramolecular complexes is very different from the values collected by Kirby for covalent bond formation (Fig. 8B and C). The values of EM for covalent bond formation are generally much higher than for noncovalent interactions and cover a much wider range of values (10 —10 M). 

Figure 3 Exclusively enthalpy-driven complexes (a) biotin-streptavidin complex as one of the tightest binding biomolecular systans, achieving an extraordinarily high affinity of 10 M through noncovalent interactions (created by the PyMol software based on PDB entry 2izf) (b) CB[7] complex with l,l -bis(trimethylammoniomethyl)ferrocene as the tightest man-made supramolecular complex that also achieves an extraordinarily high affinity of 10 M through noncovalent interactions.

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