Hi Sreetama,

The water S-gamma distance made me think that it might be a cysteine beta-mercaptoethanol adduct. Try building CME instead of CSO.

Cheers,
Robbie

Dear Users,

I am solving a structure from x-ray diffraction data (1.62A resolution).

The protein has a single cysteine residue (which is also the catalytic residue), and it has a positive density on it (fig 1; R/Rfree = 16.88/19.94). The positive density is retained upto 11.5 sigma level.

Modelling with water retains the positive density (fig 2; R/Rfree = 16.85/19.94) upto 5.2 sigma level.

Modelling with CSO (S-hydroxycysteine, fig 3, R/Rfree = 16.82/ 19.81) produces partial positive and negative densities, which are retained upto 5 sigma. Moreover, after real-space refinement in coot followed by refinement in refmac, the N-terminus of CSO is not bonded to the preceding residue, nor is its C-terminus bonded to the succedding residue.

All maps are contoured at 1sigma (2Fo-Fc map) and 3sigma (fo-fc map).

The protein preparation contained Tris buffer at pH 7.2, NaCl, glycerol and beta-mercaptoethanol (2mM), while the crystallization condition contained citric acid (pH 3.5) and ammonium sulfate.

Please suggest how to interpret the data.

thanking in advance,

sreetama