1,330
edits
Properties of proteins: Difference between revisions
CSO CSX
(CSO CSX) |
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A specific case which shows that Tm does not need to be high: the protein with PDB-ID 1ofc had a melting temperature of 37°C (from CD), which was supported by the fact that it did not express in E.coli at that temperature. | A specific case which shows that Tm does not need to be high: the protein with PDB-ID 1ofc had a melting temperature of 37°C (from CD), which was supported by the fact that it did not express in E.coli at that temperature. | ||
At 20°C it expressed to about 60mg / (liter LB), could be concentrated to more than 100mg/ml, crystallised at room temperature and diffracted to 1.9A. The initial purification steps were done at 4°C. | At 20°C it expressed to about 60mg / (liter LB), could be concentrated to more than 100mg/ml, crystallised at room temperature and diffracted to 1.9A. The initial purification steps were done at 4°C. | ||
== Modifications of amino acids == | |||
* instead of CYS you might encounter S-hydroxycysteine (CSO) or S-oxycysteine (CSX). The only difference, crystallographically, is that the CSO S-O bond is about 1.78A and the CSX S-O bond is about 1.50A. You may not be able to differentiate this difference in your electron density maps. A SH - HOH contact should be considerably longer than 1.8 A between heavy atoms, certainly more like 3.0A+/-. You can substitute either CSO or CSX for CYS in Coot by deleting the CYS residue and then using File...Get Monomer and typing in either CSO or CSX. A "surprise CSO" residue was encountered when solving the structure of 3UAO. The protein had been stored in a non-reducing medium, resulting in the oxidation of the active site Cys residue. The electron density near Cys was too close to be a water molecule, but CSO modeled nicely. | |||