| Popis: |
IbpA and IbpB (inclusion body binding proteins A and B) are two small heat shock proteins in E. coli. Earlier studies report that IbpB has holdase property by which it binds denatured, aggregate-prone proteins forming stable complexes, but has no foldase property by which it can refold denatured, unfolded proteins. This study is conducted to investigate whether IbpA also has the holdase property, how the holdase activity of IbpB is modulated by the presence of IbpA, and if IbpA and IbpB, individually or in combination, have any foldase property on denatured proteins after prolonged incubation. Our results, based on the techniques of spectrophotometry, spectrofluorimetry, HPLC, gel electrophoresis and DLS show that a) IbpA possesses holding chaperone activity, somewhat less than that of IbpB and presence of both IbpA and IbpB has synergistic effect on holdase activity; as measured from the inhibition of aggregation of DTT-denatured insulin B chains in the presence of IbpA, IbpB and IbpA+IbpB (IbpAB) and b) both IbpA and IbpB has in vitro protein folding property, as measured from the gain in activity of the denatured alkaline phosphatase (denatured either by guanidine hydrochloride or heat) after incubation with IbpA, IbpB, or IbpAB for a prolonged period of about 6 hr. To conclude briefly, it can be stated that E. coli small heat-shock proteins IbpA and IbpB have both holding and folding chaperone activities on denatured proteins, the activities being maximum at 500C and the effects are synergistic when IbpA and IbpB act in combination. |
