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Extracellular proteins of Lactobacillus crispatus enhance activation of human plasminogen

Veera Hurmalainen^1,

Sanna Edelman^1,

¹ General Microbiology, Faculty of Biosciences, PO Box 56, FIN00014 University of Helsinki, Finland
² Protein Chemistry Unit, Institute of Biomedicine/Anatomy, PO Box 63, FIN00014 University of Helsinki, Finland

Correspondence
Timo K. Korhonen
timo.korhonen{at}helsinki.fi

The abundant proteolytic plasminogen (Plg)/plasmin system is important in several physiological functions in mammals and also engaged by a number of pathogenic microbial species to increase tissue invasiveness or to obtain nutrients. This paper reports that a commensal bacterium, Lactobacillus crispatus, interacts with the Plg system. Strain ST1 of L. crispatus enhanced activation of human Plg by the tissue-type Plg activator (tPA), whereas enhancement of the urokinase-mediated Plg activation was lower. ST1 cells bound Plg, plasmin and tPA only poorly, and the Plg-binding and activation-enhancing capacities were associated with extracellular material released from the bacteria into buffer. The extracellular proteome of L. crispatus ST1 contained enolase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as major components. The enolase and the GAPDH genes of ST1 were cloned, sequenced and expressed in recombinant Escherichia coli as His₆-fusion proteins, which bound Plg and enhanced its activation by tPA. Variable levels of secretion of enolase and GAPDH proteins as well as of the Plg activation cofactor function were detected in strains representing major taxonomic groups of the genus Lactobacillus. So far, interference with the Plg system has been addressed with pathogenic microbes. The results reported here demonstrate a novel interaction between a member of the microbiota and a major proteolytic system in humans.

The GenBank/EMBL/DDBJ accession numbers for the nucleotide sequences of L. crispatus ST1 gap and eno determined in this paper are AJ849470 and AJ849471.

These authors contributed equally to this work.

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