The Evolution and Function of Co-Chaperones in Mitochondria - The Networking of Chaperones by Co-chaperones - page 210

Tim44 enabled the existing Hsp70 (Ssc1) to be recruited as a protein import motor.
That this motor is truly ubiquitous in eukaryotes is made certain from the finding
of Pam18 in the anaerobic protists Giardia intestinalis and Trichomonas vaginalis
(Dolezal et al. 2005 ).
In the course of evolution, the progenitor DnaK-type chaperone has been modi-
fied to perform novel functions: protein import and FeS cluster assembly. In some
organisms such as Saccharomyces cerevisiae, two isoforms of the DnaK ancestor
have specialized to perform one of these novel tasks, Ssc1 mediating protein import
and Ssq1 mediating FeS cluster assembly. It is intriguing that a novel co-chaperone,
Zim17, has arisen to stabilize mitochondrial (and chloroplast) Hsp70 chaperones. It
is not clear why the Hsp70s in organelles of endosybiotic origin require their struc-
ture to be enforced in a manner so distinct from their counterparts prokaryotes, and
in other eukaryotic organelles.
Acknowledgements The text and figure in this chapter contain sections reproduced with kind
permission from Springer Science + Business Media: Networking of Chaperones by Co-chaper-
ones; Chap. 9: The evolution and function of co-chaperones in mitochondria; 2007; pp. 99-108;
Dejan Bursać, and Trevor Lithgow.
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