Anchorage of cyclodextrin glucanotransferase on the outer membrane of Escherichia coli

The gene encoding cyclodextrin glucanotransferase (CGTase) was successfully cloned from B. macerans by PCR. A recombinant plasmid pCS005 with a gene encoding the Lpp-OmpA-CGTase trifusion protein was constructed and transformed into E coli for the surface display of CGTase. Results of immunoblotting analysis and protease accessibility on the fractionated cell membranes confirmed that the Lpp-OmpA-CGTase trifusion protein was successfully anchored on the outer membrane of E coli. However, only 50% of the membrane-anchored trifusion proteins were displayed on the outer surface of E. coli with the remaining 50% untranslocated. The low efficiency of surface display is attributed to the large size of CGTase. Only a trace amount of CGTase activity was detected for both the whole cells and the cell debris fractions. Because the results of the protease accessibility study suggested that the trypsin-resistant conformation of CGTase was preserved in the membrane-anchored CGTase, we believe that the lack of enzyme activity is mainly due to the inaccessibility of the CGTase active site, near the N-terminus, for substrate molecules. It can be estimated that the critical size for surface display of protein in E. coli is approximately 70 kDa. (C) 2002 Wiley Periodicals, Inc.