Hi Sam,
Did you try searching for Se sites? If you did and found no reliable sites or found sites that did not give interpretable maps or used different programs to find sites and did not see consistent sites, then it could be that your Se sites could be in less ordered or surface exposed and flexible portions of the protein. In this case, you could see Se in an excitation scan (as it is present in the protein) but may not be able to reliable locate their positions.
You can quickly assess this by multiple sequence alignments or structural comparisons and if your Met residues are in regions of low conservation, this could be the case. However, if you have numerous Met it is expected that at least some of them will be conserved and well-ordered and you should be able to find them.
Thanks,
Debanu
> On Jun 1, 2016, at 4:17 PM, Sam Jun <[log in to unmask]> wrote:
>
> Hello, all.
>
> I'm processing my recently collected data set which is SeM labeled for anomalous signal, but it seems like there is no anomalous signal present in my data. Does anyone had this problem or know what I did wrong?
> I collected all 360 degree (oscillation of 1 degree, 2 second exposure for each, 0.979 Angstrom) for three SeM protein crystals that I had.
> When I did energy scan prior to the data collection, there was a good absorption edge at the expected wavelength (0.979A f'=-8.95, f"4.053).
> Thus, I know Se is present, but after index and scale via HKL2000, I got chi^2 = 1 across all resolutions.
> As far as I know, chi^2 for anomalous should show dependence to resolution if it is present.
> Have I done something wrong such as turning on a wrong tab during data processing? or Se crystal can have no anomalous signal?
>
> PS. for scaling, [default setting + anomalous + no merge original index] was used.
>
> If anybody have any idea, please let me know. Thank you.
>
> Sincerely,
>
> Sam
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