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Journal of Bacteriology, March 2009, p. 1641-1649, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01285-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Membrane Lipoprotein LppX of Paenibacillus sp. Strain W-61 Serves as a Molecular Chaperone for Xylanase of Glycoside Hydrolase Family 11 during Secretion across the Cytoplasmic Membrane ^,

Mutsumi Fukuda,^1, Seiji Watanabe,^1,, Jun Kaneko,¹ Yoshifumi Itoh,^1, and Yoshiyuki Kamio^1,2*

Laboratory of Applied Microbiology, Department of Microbial Biotechnology, Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori Amamiyamachi, Aobaku, Sendai 981-8555,¹ Department of Human Health and Nutrition, Graduate School of Comprehensive Human Sciences, Shokei Gakuin University, Yurigaoka 4-10-1, Natori 981-1295, Japan²

Received 12 September 2008/ Accepted 9 December 2008

Paenibacillus sp. strain W-61, which can utilize xylan as the sole source of carbon and energy, produces extracellular xylanases 1 and 3 (Xyn1 and Xyn3) and cell surface xylanase 5. In this study we found that lppX, immediately downstream of xyn1, encodes a lipoprotein located on the outer layer of the cytoplasmic membrane and that the LppX lipoprotein is essential for the secretion of active Xyn1 across the cytoplasmic membranes. In Escherichia coli, wild-type LppX was destined for the inner layer of the outer membrane. Mutant LppX(C19A), in which Cys-19, a possible lipomodification residue, is replaced with Ala, was located in the periplasm without being anchored to the membranes. Another mutant, LppX(S20D S21D), with substitutions of Asp for Ser-20 and Ser-21 (conversion to an Asp-Asp signal for sorting to the inner membrane), resided on the outer layer of the inner membrane, demonstrating that LppX has the sorting property of a lipoprotein. E. coli harboring both xyn1 and lppX secreted active Xyn1 into the periplasm. In contrast, E. coli carrying xyn1 alone failed to do so, accumulating inactive Xyn1 in the cytoplasmic membranes. Exogenous LppX(C19A) liberated the inactive Xyn1, which had been stagnating in the inner membrane, into the medium as an active enzyme. Thus, we propose that LppX is a novel type of lipoprotein that assists Xyn1 in making the proper fold necessary for traveling across the cytoplasmic membranes to be secreted as an active enzyme.

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* Corresponding author. Mailing address: Department of Human Health and Nutrition, Graduate School of Comprehensive Human Sciences, Shokei Gakuin University, Yurigaoka 4-10-1, Natori 981-1295, Japan. Phone and fax: 81-22-381-3347. E-mail: ykamio{at}shokei.ac.jp

Published ahead of print on 22 December 2008.

Supplemental material for this article may be found at http://jb.asm.org/.

M.F. and S.W. contributed equally to this work. Y. Itoh passed away on 4 October 2008.

Present address: Central Research Institute, Mizkan Group Co. Ltd., Handa 475-8585, Japan.

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Journal of Bacteriology, March 2009, p. 1641-1649, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01285-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.