I expressed my protein in cell free with wheat germ, and after purification on streptag with (2,5mM, elution) i observed 2 bands on gels at the same weight.
I have already expressed the protein and it didn't show 2 bands.
Last time i eluted with 5mM of desthiobiotin. And the difference in buffer is, for the present purification i added 250µM of TCEP and 0.1% MNG3 instead of 0.01% for the first one.
The protein is in: Tris-HCl 100 NaCl150 Zn20µM TCEP250µM MNG3 0.1%.
NB: In litterature, the protein tend to forms oligomers