Photoinduced aggregation of a model antibody-drug conjugate.

During synthesis, purification, and especially storage, antibody-drug conjugates (ADCs) may be exposed to various types of light. Several of the drugs commonly conjugated to antibodies contain photosensitive functional groups. Exposure to light could generate an excited state of the drug that subsequently triggers drug and/or protein degradation.

New paradigm for allosteric regulation of Escherichia coli aspartate transcarbamoylase.

For nearly 60 years, the ATP activation and the CTP inhibition of Escherichia coli aspartate transcarbamoylase (ATCase) has been the textbook example of allosteric regulation. We present kinetic data and five X-ray structures determined in the absence and presence of a Mg(2+) concentration within the physiological range. In the presence of 2 mM divalent cations (Mg(2+), Ca(2+), Zn(2+)), CTP does not significantly inhibit the enzyme, while the allosteric activation by ATP is enhanced.

ViewMotions Rainbow: a new method to illustrate molecular motions in proteins.

The biological functions of many enzymes are often coupled with significant conformational changes. The end states of these conformational changes can often be determined by X-ray crystallography. These X-ray structures are snapshots of the two extreme conformations in which the macromolecule exists, but the dynamic movements between the states are not easily visualized in a two-dimensional illustration.

Selectivity of the highly preorganized tetradentate ligand 2,9-di(pyrid-2-yl)-1,10-phenanthroline for metal ions in aqueous solution, including lanthanide(III) ions and the uranyl(VI) cation.

Some metal ion complexing properties of DPP (2,9-Di(pyrid-2-yl)-1,10-phenanthroline) are reported with a variety of Ln(III) (Lanthanide(III)) ions and alkali earth metal ions, as well as the uranyl(VI) cation. The intense π-π* transitions in the absorption spectra of aqueous solutions of 10(-5) M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln(III) (Ln = lanthanide) ions. It was found that log K(1)(DPP) for the Ln(III) ions has a peak at Ln(III) = Sm(III) in a plot of log K(1) versus 1/r(+) (r(+) = ionic radius for 8-coordination).

Metal ion involvement in the allosteric mechanism of Escherichia coli aspartate transcarbamoylase.

Escherichia coli aspartate transcarbamoylase (ATCase) allosterically regulates pyrimidine nucleotide biosynthesis. The enzyme is inhibited by CTP and can be further inhibited by UTP, although UTP alone has little or no influence on activity; however, the mechanism for the synergistic inhibition is still unknown. To determine how UTP is able to synergistically inhibit ATCase in the presence of CTP, we determined a series of X-ray structures of ATCase·nucleotide complexes.

A second allosteric site in Escherichia coli aspartate transcarbamoylase.

Escherichia coli aspartate transcarbamoylase is feedback inhibited by CTP and UTP in the presence of CTP. Here, we show by X-ray crystallography that UTP binds to a unique site on each regulatory chain of the enzyme that is near but not overlapping with the known CTP site. These results bring into question all of the previously proposed mechanisms of allosteric regulation in aspartate transcarbamoylase.

Crystallographic snapshots of the complete catalytic cycle of the unregulated aspartate transcarbamoylase from Bacillus subtilis.

Here, we report high-resolution X-ray structures of Bacillus subtilis aspartate transcarbamoylase (ATCase), an enzyme that catalyzes one of the first reactions in pyrimidine nucleotide biosynthesis. Structures of the enzyme have been determined in the absence of ligands, in the presence of the substrate carbamoyl phosphate, and in the presence of the bisubstrate/transition state analog N-phosphonacetyl-L-aspartate. Combining the structural data with in silico docking and electrostatic calculations, we have been able to visualize each step in the catalytic cycle of ATCase, from the ordered binding of the substrates, to the formation and decomposition of the tetrahedral intermediate, to the ordered release of the products from the active site.

Enhanced metal ion selectivity of 2,9-di-(pyrid-2-yl)-1,10-phenanthroline and its use as a fluorescent sensor for cadmium(II).

The metal ion complexing properties of the ligand DPP (2,9-di-(pyrid-2-yl)-1,10-phenanthroline) were studied by crystallography, fluorimetry, and UV-visible spectroscopy. Because DPP forms five-membered chelate rings, it will favor complexation with metal ions of an ionic radius close to 1.0 A.