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We report the 3.4 angstrom crystal structure of a catalytically active group I intron splicing intermediate containing the complete intron, both exons, the scissile phosphate, and all of the functional groups implicated in catalytic metal ion coordination, including the 2'-OH of the terminal guanosine. This structure suggests that, like protein phosphoryltransferases, an RNA phosphoryltransferase can use a two-metal-ion mechanism. Two [Mg.sup.2+] ions are positioned 3.9 angstroms apart and are directly coordinated by all six of the biochemically predicted ligands. The evolutionary convergence of RNA and protein active sites on the same inorganic architecture highlights the intrinsic chemical capacity of the two-metal-ion catalytic mechanism for phosphoryl transfer., Divalent metal ions are used in the active sites of a variety of protein phosphoryltransfer enzymes, including those required for replication, transcription, and cell signaling (1-3). Structural and biochemical studies [...]

Clusters of metal ions are a class of compounds actively investigated for their magnetic properties, which should gradually change from those of simple paramagnets to those of bulk magnets. However, their interest lies in a number of different disciplines: chemistry, which seeks new synthetic strategies to make larger and larger clusters in a controlled manner; physics, which can test the validity of quantum mechanical approaches at the nanometer scale; and biology, which can use them as models of biomineralization of magnetic particles., The prefix nano- seems to be the theme of the Last decade of this century, allowing us new perspectives in many different fields. Nanoscale electronics is coming of age, but [...]

The peptide [α.sub.4] is a designed four-helix bundle that contains a highly simplified hydrop core composed exclusively of leucine residues; Its tertiary structure is therefore largely dictated by hydrophobic forces. This small protein adopts a structure with properties intermediate between those of the native and molten globule states of proteins: it is compact, globular, and has very stable helices, but its apolar side chains are mobile and not as well packed as in many natural proteins. To induce a more native-like state, two [Zn.sup.2+]-binding sites were introduced into the protein, thereby replacing some of the nonspecifi hydrophobic interactions with more geometrially restrictive metal-ligand interactions. in the metal-bound state, this protein has properties that approach those of native proteins. Thus, hydrophobic interactions alone are sufficient to drive polypeptide chain folding nearly to completion, but specific interactions are required for a unique structure., Studies of natural proteins and their variants have suggested that proteins fold via intermediates (1) stabilized by the collapse of their hydrophobic groups (2). The native structure would then form [...]