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READ Xo4 latest papers

2 NUCLEATING AGENTS

Xo4/Crystallophore additives provide new crystallization conditions but also improve the quality of the crystals obtained.

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2 PHASING AGENTS

Xo4/Crystallophore overcome the tedious and time-consuming work of seleno-methionine labelling or of heavy-atom incorporation.

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Browse our technotes to choose the right product/protocol

Tb-Xo4 technotes

Tb-Xo4 acts as a strong Nucleating Agent providing new crystallisation conditions and generally leading to the formation of bigger Tb-Xo4 derivatized crystals, ready-to-use for X-ray diffraction. Under UV irradiation, it emits in the green (Luminescent) enabling very easy detection of the Tb-Xo4 derivatized crystal in crystallization drops. It is also a straightforward Phasing Agent facilitating crystal structure determination using SAD or MAD methods, due to the exceptional anomalous properties of f-block elements.

Tb-Xo4 User GuideTb-Xo4 MSDSTb-Xo4 PDB 7MT CIF

Lu-Xo4 technotes

Lu-Xo4 presents complementary nucleation enhancement to Tb-Xo4. Both are mainly adapted to soluble proteins and complexes. This complex is not luminescent and has been designed to improve phasing properties : its LIII absorption edge, at 1.34Å, is easily accessed with most synchrotron-radiation sources leading to an anomalous contribution of about 30e. This contribution is also important (10e) on a fixed-wavelength (1Å) beamline allowing non-optimized SAD phasing.

Lu-Xo4 User GuideLu-Xo4 MSDS

FAQ

What is the usual final concentration of Xo4 in the protein solution ?

Xo4 should be dissolved by mixing it with protein solution to reach a final concentration of 10 mM. Then the crystallization experiments should be set up by mixing a volume of this « protein + Xo4 solution » with an equal volume of precipitant solution.

What is the range of final concentrations of Xo4 in the sample ?

The proposed 10 mg/ml concentration is the optimal one. When hit is obtained, it’s possible to conduct an optimization by playing with the protein solution volume used in order to vary the Xo4 concentration from 1 to 10 mM.

Are there any problems using additives such as phosphate, EDTA or EGTA ?

There should be some competition with EDTA or EGTA to chelate the Lanthanide but we don’t know what will be the cinetic for a potential Lanthanide decorporation that could affect Xo4 efficiency. If EDTA or EGTA concentration is low (< 2 mM), this could only affect up to 20% of our Tb-Xo4 complex : the unaffected 8 mM Ln-Xo4 are then still falling inside its efficiency range.

Is there any limitation on pH or buffer composition or possible ligands in co crystallization ?

Xo4 has been designed in order to be stable and highly soluble in aqueous medium and consequently fully compatible with high throughput screening. It is stable in all crystallisation conditions that have been tested ; please note that in some cases the presence of phosphate can be detrimental to the efficiency of Xo4.

What are the preferred binding sites or amino acids for Tb-Xo4 ?

There is direct interaction between protein negatively charged residues but not only.

Are some groups of enzymes inhibited by Xo4 ?

It has never been observed but we cannot exclude it for very specific proteins.