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Applied and Environmental Microbiology, July 2005, p. 3468-3474, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3468-3474.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Enhancement of the Efficiency of Secretion of Heterologous Lipase in Escherichia coli by Directed Evolution of the ABC Transporter System

Gyeong Tae Eom,1 Jae Kwang Song,2* Jung Hoon Ahn,1 Yeon Soo Seo,1 and Joon Shick Rhee1*

Department of Biological Sciences, Korea Advanced Institute of Science and Technology,1 Applied and Engineering Chemistry Division, Korea Research Institute of Chemical Technology, Daejeon, Republic of Korea2

Received 8 September 2004/ Accepted 7 January 2005

The ABC transporter (TliDEF) from Pseudomonas fluorescens SIK W1, which mediated the secretion of a thermostable lipase (TliA) into the extracellular space in Escherichia coli, was engineered using directed evolution (error-prone PCR) to improve its secretion efficiency. TliD mutants with increased secretion efficiency were identified by coexpressing the mutated tliD library with the wild-type tliA lipase in E. coli and by screening the library with a tributyrin-emulsified indicator plate assay and a microtiter plate-based assay. Four selected mutants from one round of error-prone PCR mutagenesis, T6, T8, T24, and T35, showed 3.2-, 2.6-, 2.9-, and 3.0-fold increases in the level of secretion of TliA lipase, respectively, but had almost the same level of expression of TliD in the membrane as the strain with the wild-type TliDEF transporter. These results indicated that the improved secretion of TliA lipase was mediated by the transporter mutations. Each mutant had a single amino acid change in the predicted cytoplasmic regions in the membrane domain of TliD, implying that the corresponding region of TliD was important for the improved and successful secretion of the target protein. We therefore concluded that the efficiency of secretion of a heterologous protein in E. coli can be enhanced by in vitro engineering of the ABC transporter.

* Corresponding author. Mailing address for Joon Shick Rhee: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea. Phone: 82-42-869-2613. Fax: 82-42-869-2610. E-mail: jsrhee1{at}webmail.kaist.ac.kr. Mailing address for Jae Kwang Song: Applied and Engineering Chemistry Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong-gu, Daejeon 305-600, Korea. Phone: 82-42-860-7643. Fax: 82-42-860-7649. E-mail: ajee{at}krict.re.kr.

Applied and Environmental Microbiology, July 2005, p. 3468-3474, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3468-3474.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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