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Applied and Environmental Microbiology, August 2002, p. 3932-3942, Vol. 68, No. 8
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.8.3932-3942.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

The Peptidyl-Prolyl Isomerase Motif Is Lacking in PmpA, the PrsA-Like Protein Involved in the Secretion Machinery of Lactococcus lactis

Sophie Drouault,1,2 Jamila Anba,2 Sophie Bonneau,2,{dagger} Alexander Bolotin,2 S. Dusko Ehrlich,2 and Pierre Renault2*

Unité d'Ecologie et de Physiologie du Système Digestif,1 Unité de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas CedexFrance2

Received 16 November 2001/ Accepted 16 May 2002

The prsA-like gene from Lactococcus lactis encoding its single homologue to PrsA, an essential protein triggering the folding of secreted proteins in Bacillus subtilis, was characterized. This gene, annotated pmpA, encodes a lipoprotein of 309 residues whose expression is increased 7- to 10-fold when the source of nitrogen is limited. A slight increase in the expression of the PrsA-like protein (PLP) in L. lactis removed the degradation products previously observed with the Staphylococcus hyicus lipase used as a model secreted protein. This shows that PmpA either triggers the folding of the secreted lipase or activates its degradation by the cell surface protease HtrA. Unlike the case for B. subtilis, the inactivation of the gene encoding PmpA reduced only slightly the growth rate of L. lactis in standard conditions. However, it almost stopped its growth when the lipase was overexpressed in the presence of salt in the medium. Like PrsA of B. subtilis and PrtM of L. lactis, the L. lactis PmpA protein could thus have a foldase activity that facilitates protein secretion. These proteins belong to the third family of peptidyl-prolyl cis/trans-isomerases (PPIases) for which parvulin is the prototype. Almost all PLP from gram-positive bacteria contain a domain with the PPIase signature. An exception to this situation was found only in Streptococcaceae, the family to which L. lactis belongs. PLP from Streptococcus pneumoniae and Enterococcus faecalis possess this signature, but those of L. lactis, Streptococcus pyogenes, and Streptococcus mutans do not. However, secondary structure predictions suggest that the folding of PLP is conserved over the entire length of the proteins, including the unconserved signature region. The activity associated with the expression of PmpA in L. lactis and these genomic data show that either the PPIase motif is not necessary for PPIase activity or, more likely, PmpA foldase activity does not necessarily require PPIase activity.


* Corresponding author. Mailing address: Unité de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas Cedex, France. Phone: 33-1 34 65 24 25 27. Fax: 33-1 34 65 24 25 21. E-mail: renault{at}jouy.inra.fr.

{dagger} Present address: Unité de Pathologie Végétale, Institut National de la Recherche Agronomique, 49071 Beaucouzé, Cedex, France.


Applied and Environmental Microbiology, August 2002, p. 3932-3942, Vol. 68, No. 8
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.8.3932-3942.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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