A1 Refereed original research article in a scientific journal

Vesicle-independent extracellular release of a proinflammatory outer membrane lipoprotein in free-soluble form




AuthorsKarched M, Ihalin R, Eneslatt K, Zhong DY, Oscarsson J, Wai SN, Chen C, Asikainen SE

PublisherBIOMED CENTRAL LTD

Publication year2008

JournalBMC Microbiology

Journal name in sourceBMC MICROBIOLOGY

Journal acronymBMC MICROBIOL

Article numberARTN 18

Volume8

Number of pages14

ISSN1471-2180

DOIhttps://doi.org/10.1186/1471-2180-8-18

Web address https://bmcmicrobiol.biomedcentral.com/articles/10.1186/1471-2180-8-18


Abstract
Background: Aggregatibacter actinomycetemcomitans is an oral bacterium associated with aggressively progressing periodontitis. Extracellular release of bacterial outer membrane proteins has been suggested to mainly occur via outer membrane vesicles. This study investigated the presence and conservation of peptidoglycan-associated lipoprotein (AaPAL) among A. actinomycetemcomitans strains, the immunostimulatory effect of AaPAL, and whether live cells release this structural outer membrane lipoprotein in free-soluble form independent of vesicles.Results: The pal locus and its gene product were confirmed in clinical A. actinomycetemcomitans strains by PCR-restriction fragment length polymorphism and immunoblotting. Culturing under different growth conditions revealed no apparent requirement for the AaPAL expression. Inactivation of pal in a wild-type strain (D7S) and in its spontaneous laboratory variant (D7SS) resulted in pleiotropic cellular effects. In a cell culture insert model (filter pore size 0.02 mu m), AaPAL was detected from filtrates when strains D7S and D7SS were incubated in serum or broth in the inserts. Electron microscopy showed that A. actinomycetemcomitans vesicles (0.05-0.2 mu m) were larger than the filter pores and that there were no vesicles in the filtrates. The filtrates were immunoblot negative for a cytoplasmic marker, cyclic AMP (cAMP) receptor protein. An ex vivo model indicated cytokine production from human whole blood stimulated by AaPAL.Conclusion: Free-soluble AaPAL can be extracellularly released in a process independent of vesicles.



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