Abstract: The present invention provides methods for producing FKBP-type peptidyl-prolyl cis-trans isomerase (FkpA) polypeptides at very high levels of purity. Also provided we ultrapure FkpA and methods of using same, e.g., for use in immunoassays to show removal of FkpA from biologics produced in bacteria. In addition, the present invention provides methods of purifying polypeptides (e.g., multispecific antibodies) produced in bacteria overexpressing one or more chaperones. The methods include affinity chromatography, mixed-mode chromatography and hydrophobic interaction chromatography. in some aspects, the invention provides compositions of polypeptides (e.g., multispecific antibodies) that are essentially fee of product-specific impurities.