Thanks for the suggestions/ideas. The protein is recombinantly expressed in E.coli. It does in fact show a metal dependency. We mass spec'd the peaks once looking for phosphorylation, which was not detected, but we only got about 60-70% sequence coverage so it was not very helpful.
Quoting "Nadir T. Mrabet" <[log in to unmask]>:
> Given no info on the protein, it can be anything.
> Is it recombinant? Which host? etc.
>
> Oxydation (cys, met) is also a possibility
> By the way, deamination concerns asn and gln, not lys.
>
> Best,
>
> Nadir
>
> Pr. Nadir T. Mrabet
> Structural& Molecular Biochemistry
> Nutrigenex - INSERM U-954
> Nancy University, School of Medicine
> 9, Avenue de la Foret de Haye, BP 184
> 54505 Vandoeuvre-les-Nancy Cedex
> France
> Phone: +33 (0)3.83.68.32.73
> Fax: +33 (0)3.83.68.32.79
> E-mail: Nadir.Mrabet<at> medecine.uhp-nancy.fr
>
>
>
> On 18/02/2011 19:45, Soisson, Stephen M wrote:
>> Possibly deamidation of the protein, in particluar one or more
>> lysines. What does the Mass spec look like?
>> Cheers,
>> Steve
>>
>> ------------------------------------------------------------------------
>> *From:* CCP4 bulletin board [mailto:[log in to unmask]] *On
>> Behalf Of *Ulli Hain
>> *Sent:* Friday, February 18, 2011 12:14 PM
>> *To:* [log in to unmask]
>> *Subject:* [ccp4bb] off-topic: 2 peaks on Cation
>>
>> Hi, I was wondering if anyone had possible explanations for a
>> recombinantly expressed soluble protein that runs as 2 equal,
>> slightly overlapping peaks on a cation exhanger but as one peak on a
>> size exclusion column and same electrophoretic mobility on SDS-PAGE.
>> -Ulli
>>
>>
>> Adelaide Ulricke Hain
>> PhD Candidate
>> Johns Hopkins Bloomberg School of Public Health
>> Department of Biochemistry and Molecular Biology
>> 615 North Wolfe Street
>> Baltimore, MD 21205
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