Category Archives: poly-His purification troubleshooting

Gel bands and gel bandits

A protein ID confirmation is probably the most requested proteomics service in the facility; and it is not just a good (or ‘expensive’) idea – it could save you hours in the lab in the long run. When the MS result is not what you expected, don’t panic: use the MS information to your advantage! Knowing the parameters of interfering proteins (MW, pI, mechanism of metal ion binding) can help you to optimize or change your purification scheme.  

…Poly-His purification approach was inspired by high affinity of transition metal ions (divalent Co, Ni, Zn, and Cu) for His and Cys residues in naturally occurring proteins way back in 1975 …

What I usually see is a prominent gel band that is thought to contain a protein of interest with a poly-His purification tag which has been expressed in E.Coli and purified on an immobilized metal affinity chromatography (IMAC) column. When the protein of interest ID is confirmed, you leave me with a smile and a thank you, so read no further.

This post is for my disappointed customer whose gel band got hijacked by a bunch of E. Coli gel bandits. Having seen enough of their sneering mug shots/accession numbers, I have compiled a quick reference list of these interfering so-and-so’s from the references 1 and 2 (also included as pdf). Please note that these accession numbers are for K12, other strains will have a different accession number for the same gene product. Additional references, some of which offer solutions to the interference problem(s), are included for your enjoyment. If you encounter recurring interfering proteins in your purification system, and they are not listed here, please share this information!

Gel bandits reference list



  1. Bolanos-Garcia and Davies; Structural analysis and classification of native proteins from E. coli commonly co-purified by immobilised metal affinity chromatography. doi:10.1016/j.bbagen.2006.03.027
  2. Bartlow et al.; Identification of native Escherichia coli BL21 (DE3) proteins that bind to immobilized metal affinity chromatography under high imidazole conditions and use of 2D-DIGE to evaluate contamination pools with respect to recombinant protein expression level. doi:10.1016/j.pep.2011.04.021
  3. Robichon et al.;Engineering Escherichia coli BL21(DE3) derivative strains to minimize E.coli protein contamination after purification by immobilized metal affinity chromatography. doi:10.1128/AEM.00119-11
  4. Parsy et al.; Two-step method to isolate target recombinant protein from co-purified bacterial contaminant SlyD after immobilised metal affinity chromatography. doi:10.1016/j.jchromb.2007.03.046
  5. Block et al.; Immobilized-Metal Affinity Chromatography (IMAC): A Review. Methods in Enzymology, doi:10.1016/S0076-6879(09)63027-5

Gel bandits reference list pdf