No,  Most probably 6His tag shall not interfere in 20Kda protein.

His-tag never interfere with Western Blot, actually you can use Anti-His to detect proteins with His-tag when the expression levels are too low to be detected with Comassie staining.

Thank you Gopal and Sanfelice.

@Sanfelice: Yes true i can use Anti-His, However, my objective is to use this recombinant protein as a diagnostic antigen. This HIS tagged recombinant protein could probably be coated onto ELISA plates or onto the membrane strips for western blotting. So this HIS should not interfere with the diagnosis.

@Gopal:  Just curious to know : Is there any curoff kDa size for HIS tagged recombinant protein that below some kDa the 6XHIS will interfere. [since you replied 20kDa shall not interfere]

If the HIS tag is not important for solubility and stability of your target protein, you can remove the tag by enzyme-mediated cleavage followed by purification by size exclusion chromatography. You can separate your 20kDa protein from HIS tag by using Sephadex s75 column

Thank you Tekewe for the suggestion.

The 6x His tag should not be a problem for Western/ELISA. I have used it for proteins which were 35 kDa and 82kDa and it worked with both (in case you think there is a size constraint).

May be you can delete His-tag by enzyme-mediated cleavage followed by purification by size exclusion chromatography。

Yes removing the tag is straight forward.

Earlier, this same recombinant protein has been sent through series of restriction and purification steps to end up as a  recombinant HIS tag .

As suggested, to remove HIS,  It needs additional restriction and purification steps, which could sometimes reduce the concentration of the protein. Moreover i want a lesser purification steps for my recombinant protein without compromising the quality of the result.

So i was trying to make sure whether the presence or absence of HIS in a recombinant protein (antigen) has same result for Western/ELISA

Thank you for your suggestion,