activity of Acanthamoeba was first reported (I believe) in 1988
in the context of pathogenesis (Ferrante
although protease activity had been identified prior to its involvement
in pathogenesis was known.
Collagenase activity was later discovered in culture supernatant in
which Acanthamoeba had been cultured (He
et al, 1990)
in addition to amoeba, but not in cysts (Mitro
et al, 1994).
All of the Acanthamoeba
spp that I have so far isolated have isolated and tested contain a
protease active against collagen (see Amoeba methods) that is present in
the growth medium presumably having been secreted by the amoebae.
The proteases secreted from Acanthamoeba seem to be extremely
variable in character with a range of molecular weights being reported
as well as a range of physical characteristics (Table 1). Various
proteases have described, even from the same strain including serine,
cysteine and metalloproteinases (Mitro
et al, 1994;
al, 1998; Alfieri et al, 2000).
It seems that serine type proteases are especially abundant in
secretions from Acanthamoeba, and a subtilisin-like serine
proteinase has been cloned from Acanthamoeba healyi (Hong,
et al, 2000)
The fact that
all Acanthamoeba strain seem to secrete proteases whither or not
they happen to be pathogenic, raises the question of why Acanthamoeba
(and other amoeba) secrete proteases. It has been suggested that Acanthamoeba
is just a "messy eater" spilling out hydrolytic enzymes from
the phagolysosome in the course of membrane turnover (Homan
& Bowers, 1984). What ever the
purpose in protease secretion, it is certain that the proteases do have
the potential to degrade cornea once an infection of Acanthamoeba
has been established, and it is believed that the proteolytic activity
is a key fact in Acanthamoeba keratitis (see Acanthamoeba
pathogenesis). It has been suggested that the cytopathogenic
activity found in culture supernatant from Acanthamoeba that
seems to work through induction of apoptosis (Alizadeh
et al, 1994)
is actually the protease .
The pH optima
is reported to be acidic (pH 5.0 - 5.5) (Alfiero
et al, 2000;
Correia, C.E.B., Motegi, S.A., & Pral, E.M.F. (2000). "Proteinase
activities in total extracts and in medium conditioned by Acanthamoeba
polyphaga trophozoites." J.Parasitol. 86, 220-227.
Alizadeh, H., Pidherney, M. S.,
McCulley, J. P. & Niederkorn, J. Y. (1994) Apoptosis as a mechanism
of cytolysis of tumor cells by a pathogenic free-living amoeba, Infect.Immun.
Cao, Z., Jefferson, D. M. &
Panjwani, N. (1998) Role of carbohydrate-mediated adherence in
cytopathogenic mechanisms of Acanthamoeba, J.Biol.Chem. 273,
Ferrante, A. & Bates, E. J. (1988)
Elastase in the pathogenic free-living amoebae Naegleria and Acanthamoeba,
Infect.Immun. 56, 3320-3321.
He, Y.-G., Niederkorn, J. Y., McCulley,
J. P., Stewart, G. L., Meyer, D. R., Silvany, R. & Dougherty, J.
(1990) In vivo and in vitro collagenolytic activity of Acanthamoeba
castellanii, In.Oph.Vis.Sci. 31, 2235-2240.
Hohman, T. C. & Bowers, B. (1984)
Hydrolase secretion is a consequence of membrane recycling, J.Cell
Biol. 98, 246-252.
Kong, H.-H., Ock, M.-S., Kim, I.-S., & Chung, D.-I. (2001).
"Isolation and characterization of a cDNA encoding a subtilisin-like
serine proteinase (AhSUB) from Acanthamoeba healyi". Mol.Biochem.Parasitol.
Mitro, K., Bhagavathiammai, A., Zhou,
O.-M., Bobbett, G., McKerrow, J. H., Chokshi, R., Chokshi, B. &
James, E. R. (1994) Partial characterization of the proteolytic
secretions of Acanthamoeba polyphaga, Exp.Parsitol. 78,
Na, B.-K., Kim, J.-C. & Song,
C.-Y. (2001) Characterization and pathogenetic role of proteinase from Acanthamoeba
castellanii., Microbial Pathogenesis. 30, 39-48.
Seo, J.-H., Yong, T.-S. & Im, K.-i.
(1991) Biochemical studies on proteinase in Acanthamoeba culbertsoni,
Yonsei Rep.Trop.Med. 22, 21-28.