Purification of recombinant L. rhamnosus GG SpaA. (a) Coomassie Blue-stained recombinant L. rhamnosus GG SpaA protein on a 12% SDS–PAGE gel. Lane 1, purified recombinant SpaA from gel-filtration chromatography; lane 2, molecular-weight markers (labelled in kDa). (b) Sephacryl S-200 (26/60) column (GE Healthcare) size-exclusion profile of SpaA. The protein peak elutes at a volume of 154 ml, which is close to the calculated weight of the monomeric protein. The positions of eluted peaks corresponding to the standards (ovalbumin, 43 kDa; carbonic anhydrase, 29 kDa) are marked with arrows.