MBP-Tagged protein degrading after expression - (Apr/04/2013 )

I am trying to do purification of a protein having MBP tag. After sonication, i am seeing a band of 42 kDa and suspecting it to be MBP breakdown product. After extensive washing with column buffer i eluted the protein with 10mM maltose and agian i am seeing multiple bands. I need to purify the protein to homogeneity for my activity assay. Please anybody who overcame this help me.

There is often endogenous MBP that is co-purified from E.coli. Is it a minor part of your purified material or a major contaminant?