The accession numbers supplied by the authors in Table 1, p. 555, were incorrect. The correct ones are given below.

MS was “invented” during the hunt for the electron, but it has come a long way since then. Jennifer Griffiths traces the history of the technique and highlights some of the great MS achievements during the past century.

In vivo, 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase catalyzes the reversible, stereospecific retro-aldol cleavage of KDPG to pyruvate and D-glyceraldehyde-3-phosphate. The enzyme is a lysine-dependent (Class I) aldolase that functions through the intermediacy of a Schiff base. Here, we propose a mechanism for this enzyme based on crystallographic studies of wild-type and mutant aldolases. The three dimensional structure of KDPG aldolase from the thermophile Thermotoga maritima was determined to 1.9A. The structure is the standard alpha/beta barrel observed for all Class I aldolases. At the active site Lys we observe clear density for a pyruvate Schiff base. Density for a sulfate ion bound in a conserved cluster of residues close to the Schiff base is also observed. We have also determined the structure of a mutant of Escherichia coli KDPG aldolase in which the proposed general acid/base catalyst has been removed (E45N). One subunit of the trimer contains density suggesting a trapped pyruvate carbinolamine intermediate. All three subunits contain a phosphate ion bound in a location effectively identical to that of the sulfate ion bound in the T. maritima enzyme. The sulfate and phosphate ions experimentally locate the putative phosphate binding site of the aldolase and, together with the position of the bound pyruvate, facilitate construction of a model for the full-length KDPG substrate complex. The model requires only minimal positional adjustments of the experimentally determined covalent intermediate and bound anion to accommodate full-length substrate. The model identifies the key catalytic residues of the protein and suggests important roles for two observable water molecules. The first water molecule remains bound to the enzyme during the entire catalytic cycle, shuttling protons between the catalytic glutamate and the substrate. The second water molecule arises from dehydration of the carbinolamine and serves as the nucleophilic water during hydrolysis of the enzyme-product Schiff base. The second water molecule may also mediate the base-catalyzed enolization required to form the carbon nucleophile, again bridging to the catalytic glutamate. Many aspects of this mechanism are observed in other Class I aldolases and suggest a mechanistically and, perhaps, evolutionarily related family of aldolases distinct from the N-acetylneuraminate lyase (NAL) family.

No abstract

The realm of The nanopore Interest in nanoscale research has skyrocketed, and the humble pore has become a king.Jennifer Griffiths little more than 10 years ago, a group of scientists made a discovery that would revolutionize the way DNA was sequenced-or so they hoped. In their 1996 paper (1), the team, which included John Kasianowicz of the U.S. National Institute of Standards and Technology, Daniel Branton of Harvard University, and David Deamer of the University of California Santa Cruz, showed that they could use an electric field to drive single-stranded DNA and RNA molecules into the aperture of a proteinaceous transmembrane ion channel and use the pore as a sensor. "It was very clearly allowing us to detect individual [DNA] molecules and [to] begin to learn something about the character of these molecules," says Branton. "The very first thing we noticed was that we could obviously determine the length or the size of the molecule C. Dekker, TU DelfT/Tremani J A n u A r y 1 , 2 0 0 8 / A n A l y t i c A l c h e m i S t r y 2 3