The peptidyl-prolyl isomerase motif is lacking in PmpA, the PrsA-like protein involved in the secretion machinery of Lactococcus lactis.
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.
Drouault
Sophie
S
Unité d'Ecologie et de Physiologie du Système Digestif. Unité de Génétique Microbienne, Institut National de la Recherche Agronomique, 78352 Jouy en Josas Cedex, France.
Anba
Jamila
J
Bonneau
Sophie
S
Bolotin
Alexander
A
Ehrlich
S Dusko
SD
Renault
Pierre
P
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D013294:Lactococcus lactis / Q000737:chemistry* / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D008049:Lipase / Q000378:metabolism; D008074:Lipoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D019696:Peptidylprolyl Isomerase / Q000737:chemistry*; D017510:Protein Folding; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013291:Streptococcus / Q000737:chemistry / Q000378:metabolism; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D008074:Lipoproteins; D008565:Membrane Proteins; C082160:prsA protein, bacteria; D008049:Lipase; D019696:Peptidylprolyl Isomerase