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Maaike M E de Backer

Publications and source records attributed to Maaike M E de Backer.

2 recordsLinked to original sources

Automatic structure determination based on the single-wavelength anomalous diffraction technique away from an absorption edge.

The phasing of macromolecular structures based on the use of the single-wavelength anomalous diffraction method has recently enjoyed a revival. Here, additional evidence is provided that the method may be successfully applied at wavelengths remote from the absorption edge of interest and that it is in principle applicable to a large number of systems. This opens up the possibility of rapid and reliable automatic de novo structure determination using simple experimental configurations with no need for wavelength tunability or absorption-edge scanning. The method should therefore be exploitable at most synchrotron beamlines. The effects of data completeness and multiplicity on the quality of the phases obtained are discussed as are the prospects for the automation of macromolecular structure solution based on the experimental protocols described.

Alkaline Phosphatase↗

Ligand-binding and metal-exchange crystallographic studies on shrimp alkaline phosphatase.

Alkaline phosphatases (APs) are homodimeric metalloenzymes that catalyze the hydrolysis and transphosphorylation of phosphate monoesters. Each monomer contains a metal-binding triad that for optimal activity is usually occupied by two zinc ions and one magnesium ion. The recently determined crystal structure of cold-active shrimp alkaline phosphatase (SAP) was, however, fully occupied by zinc ions. This paper describes a metal-exchange experiment in which the zinc ion in one binding site (referred to as the M3 site) is replaced by magnesium. Crystal structures revealed a concomitant structural change: the metal exchange causes movement of a ligating histidine into a conformation in which it does not coordinate to the metal ion. The M3 site is relevant to catalysis: its occupation by magnesium is postulated to favour catalysis and it has been suggested to be a regulatory site for other APs. Further crystallographic studies show that ligand binding can induce a conformational change of an active-site arginine from a 'non-docked' (non-interacting) to a 'docked' conformation (interacting with the ligand). The first conformation has only been observed in SAP, while the latter is common in available AP structures. The observation that the arginine does not always bind the substrate may explain the increased catalytic efficiency that is generally observed for cold-active enzymes.

Alkaline Phosphatase↗