NO binding to the proapoptotic cytochrome c-cardiolipin complex.

Cytochrome c is a heme protein that is localized in the compartment between the inner and outer mitochondrial membranes where it functions to transfer electrons between complex III and complex IV of the respiratory chain. It can also form an intimate association with the mitochondrion-specific phospholipid cardiolipin that induces a conformational change in the protein enabling it to act as a peroxidase catalyzing the oxidation of cardiolipin and thereby instigating a chain of events that leads to apoptosis. Unlike the native protein, cytochrome c within the complex binds ligands rapidly; in particular, NO can coordinate to either the ferric or ferrous iron of the heme. Remarkably, in the ferrous form, NO binds preferentially to the proximal side of the heme and thus behaves in a way similar to cytochrome c'-type proteins and to guanylate cyclase. The implications of NO binding to the proapoptotic cytochrome c/cardiolipin complex are discussed in terms of modulating the apoptotic response and buffering NO concentrations. Insights into the structure of the complex are provided by comparison with cytochrome c' for which X-ray structures are available.

Design and chance in the self-assembly of macromolecules.

The principles of self-assembly are described for naturally occurring macromolecules and for complex assemblies formed from simple synthetic constituents. Many biological molecules owe their function and specificity to their three-dimensional folds, and, in many cases, these folds are specified entirely by the sequence of the constituent amino acids or nucleic acids, and without the requirement for additional machinery to guide the formation of the structure. Thus sequence may often be sufficient to guide the assembly process, starting from denatured components having little or no folds, to the completion state with the stable, equilibrium fold that encompasses functional activity. Self-assembly of homopolymeric structures does not necessarily preserve symmetry, and some polymeric assemblies are organized so that their chemically identical subunits pack stably in geometrically non-equivalent ways. Self-assembly can also involve scaffolds that lack structure, as seen in the multi-enzyme assembly, the degradosome. The stable self-assembly of lipids into dynamic membraneous sheets is also described, and an example is shown in which a synthetic detergent can assemble into membrane layers.

Paramagnetic resonance of biological metal centers.

The review deals with recent advances in magnetic resonance spectroscopy (hf EPR and NMR) of paramagnetic metal centers in biological macromolecules. In the first half of our chapter, we present an overview of recent technical developments in the NMR of paramagnetic bio-macromolecules. These are illustrated by a variety of examples deriving mainly from the spectroscopy of metalloproteins and their complexes. The second half focuses on recent developments in high-frequency EPR spectroscopy and the application of the technique to copper, iron, and manganese proteins. Special attention is given to the work on single crystals of copper proteins.