Chaperonin—Co-chaperonin Interactions - The Networking of Chaperones by Co-chaperones - page 165

during its transition from a mammalian to an insect vector (Maresca and Carratu
1992 ). Induction of Hsp60 was found to occur during the entire course of infection
of Trypanosoma brucei , a protozoan parasite responsible for causing sleeping sick-
ness in humans (Radwanska et al. 2000 ).
The chloroplast type I chaperonin complex (Cpn60) is structurally similar to
GroEL and also forms two stacked heptameric rings (Tsuprun et al. 1991 ), however
these are composed of two different subunit types, Cpn60α and Cpn60ʲ (Martel
et al. 1990 ) which are ~ 50 % identical to each other (Hill and Hemmingsen 2001 ).
Arabidopsis thaliana encodes several Cpn60α and Cpn60ʲ families and both are
required for plastid division (Suzuki et al. 2009 ). A unique chaperonin subunit pres-
ent in A. thaliana confers substrate specificity, while the dominant subunits retain
housekeeping functions (Peng et al. 2011 ).
Specific Functions of Eukaryotic Group I Co-chaperonins
A single copy of the Cpn10 co-chaperonin is present in the mitochondria of yeast
and mammals, in contrast to chloroplasts that have two different co-chaperonin
homologs (Rospert et al. 1993 ; Hansen et al. 2003 ). The chloroplast co-chaperonins
are varied with cpn10 encoding the conventional 10 kDa protein that is similar
in structure and function to GroES, as well as cpn20 encoding tandem fusions of
Cpn10 domains that form tetrameric ring structures that function with GroEL and
Cpn60 (Bertsch et al. 1992 ; Koumoto et al. 2001 ; Sharkia et al. 2003 ). Interestingly,
the green alga Chlamydomonas reinhardtii has three co-chaperonins, Cpn10, Cpn20
and Cpn23 that are individually non-functional (Tsai et al. 2012 ). In studies using
recombinant co-chaperonins of A. thaliana and C. reinhardtii hetero-oligomeric
ring complexes formed by combinations of Cpn10, Cpn20 and Cpn23 were able to
serve as co-chaperonins in order to perhaps modify the chaperonin folding cage for
specific client proteins (Tsai et al. 2012 ).
Whilst our understanding of the roles of human Hsp10 in disease continues to
receive research attention, little is known about the roles of its homologues in viru-
lence and pathogenicity of protozoan parasites affecting human health; and they
may interact with the human chaperone system. The first protozoan CPN10 pro-
tein characterised was from Leishmania donovani and was shown to interact with
CPN60.2 with increased concentrations detected during the amastigote stage of the
lifecycle (Zamora-Veyl et al. 2005 ). Cpn20 proteins were known to exist only in
chloroplasts, however sequencing of the malarial genome revealed a single Cpn20
protein which correlates with the algal origin of the parasite (Sato and Wilson 2005 ;
Janouskovec et al. 2010 ). Since the Plasmodium falciparum genome encodes only
one cpn20 gene, it functions as a homo-oligomeric co-chaperonin that can function-
ally replace GroES (Vitlin Gruber et al. 2013b ). Characterisation of HSP10 from
Strongyloides ratti, an intestinal nematode infecting humans, revealed a strong im-
munogenic response and the inability to bind to S. ratti HSP 60 provided evidence
of a role in host-parasite interactions (Tazir et al. 2009 ).