The potent bone-resorbing mediator of Actinobacillus actinomycetemcomitans is homologous to the molecular chaperone GroEL.

Abstract

Actinobacillus actinomycetemcomitans is a Gram-negative bacterium implicated in the pathology of localized juvenile periodontitis, a condition involving rapid destruction of alveolar bone. We have established that gentle extraction of this bacterium in saline releases a proteinaceous fraction (which we have termed surface-associated material [SAM]) which has potent osteolytic activity in the murine calvarial bone resorption assay. Fractionation of the SAM has now revealed that activity is associated with a 62-kD protein. This bone-resorbing activity can be blocked by a monoclonal antibody (raised to the whole bacterium) that is claimed to recognize a protein homologous to the Escherichia coil molecular chaperone GroEL. Purification of this bone-resorbing protein to homogeneity has been achieved by a combination of anion exchange, gel filtration, and ATP-affinity chromatography and the NH2-terminal sequence shows > 95% homology to E.

Unfolding the relationship between secreted molecular chaperones and macrophage activation states

“…The author's group have shown a relationship between circulating Hsp60 and cardiovascular disease, and this may relate to the influence of these proteins on macrophage function (Lewthwaite et al 2002b;Halcox et al 2005;Shamaei-Tousi et al 2007b) The in vivo breakdown of bone is driven by a specific monocyte population known as the osteoclast. Gramnegative bacterial Hsp60 proteins have been shown to stimulate both osteoclast formation and activation (Kirby et al 1995;Reddi et al 1998) as has human Hsp60 (Meghji et al 2003). However, it was found that the homologous proteins (Hsp60.2) from Mycobacterium tuberculosis and Mycobacterium leprae had no such activity (Kirby et al 1995).…”

“…Gramnegative bacterial Hsp60 proteins have been shown to stimulate both osteoclast formation and activation (Kirby et al 1995;Reddi et al 1998) as has human Hsp60 (Meghji et al 2003). However, it was found that the homologous proteins (Hsp60.2) from Mycobacterium tuberculosis and Mycobacterium leprae had no such activity (Kirby et al 1995).…”

“…Macrophage fusion is a complex process (Helming and Gordon 2008) and one of the main cell surface proteins involved in the process, dendritic cellspecific transmembrane protein (DC-STAMP), has recently been shown to be differentially regulated in osteoclasts and in macrophage giant cells (Yagi et al 2007). The finding that the Mtb Hsp60.2 protein, unlike other Hsp60 proteins, did not promote osteoclast formation and bone remodelling (Kirby et al 1995) stimulated an examination of the bone destroying actions of the Mtb Hsp60.1 protein. Surprisingly, this recombinant protein did not promote osteoclast formation (Meghji et al 1997).…”

The Intercellular Signaling Activity of the Mycobacterium tuberculosis Chaperonin 60.1 Protein Resides in the Equatorial Domain

“…We then showed that the E. coli Cpn60 protein, GroEL, was a potent stimulator of bone resorption. However, neither the M. tuberculosis nor the M. leprae Cpn60.2 protein was able to induce bone resorption (22). Further investigation of the mycobacterial chaperonins revealed that neither of the two Cpn60 proteins produced by M. tuberculosis could stimulate bone resorption.…”

The Unfolding Story of the Chaperonins

“…Bacterial infections cause conlmon bone diseases such as the periodontal diseases (with a prevalence of 10-150/0 worldwide), osteolnyelitis, bacterial arthritis and tuberculosis of bone. The first evidence that cpns could cause bone pathology was the finding that the cpn 60 of the oral pathogen, Act;lZobaciIIus actill011ryceten1C0l1zitails could cause bone resorption in vitro (Kirby et al, 1995). These studies found that groEL was a potent stimulator of bone resorption but that the cpn 60 molecules of Mycobacteritl1n spp.…”