A Summary of My Current
Research Interest
Plastids and mitochondria are
"life-driving" organelles, capturing and producing energy for the
cell. These energy-generating processes underlie the workings of all cellular
events, by providing energy and products for driving the proteome networks and
by providing the regulatory signals for decision-making events. These decisions
in turn determine how proteome networks throughout the cell work under changing
environments. Whole cell events are thus driven by dynamic interacting networks
between proteomes of the nucleus and the organelles. A key mechanism for
interaction involves protein trafficking and compartmentalization. The dynamic
act of protein delivery itself (e.g., delivery of key threshold enzymes, regulators
& gatekeepers) will govern how proteome networks react and work together in
response to different needs, and more importantly, how organelles and the whole
organism develop for adaptation to the changing environment.
The process of organellar protein delivery
involves a multitude of interacting factors (located in the cytosol
and in the organelles) that attend to recognition, movement and processing.
Proteins newly made in the cytosol are delivered to
the organelles by targeting signals and then transported across organellar
membranes via analogous multi-component machineries (also called translocons). The various translocon components collaborate
to move proteins efficiently across membranes. Although most of the components
along a protein's route across the membranes have been partially characterized,
many aspects related to function remain to be defined.
Our research on functional aspects for
different plastid translocon components has unveiled further insights into
protein delivery and its influential role in the cell. Translocons
must not only attend to the act of transporting proteins but to their
ever-changing relationship with the cell. In our lab, we have observed
phenomena such as preferential import of proteins into different plastid types,
developmental changes to component levels and changes to plastid translocon
composition and cell structure in transgenic plants. We have recently observed
changes to translocon composition in response to environmental stressors (light
& cold), a phenomenon also observed for plant mitochondria. These findings
clearly illustrate that protein trafficking occupies an influential role in a
cell, responding to the cell's needs. It is now evident that these
interconnected aspects need to be investigated, the realm in which our current
research lies.
Selection of Relevant Publications
Karakasis, K., Taylor, D., Ko. K. 2007.
Uncovering a potential link between
a plastid translocon component and rhomboid proteases using yeast
mitochondria-based assays. Plant Cell Physiol. 48:655-661.
Ko, K.,
Chan, K., Karakasis, K., Pedram, B. 2006. Plastid protein
import: Coping with diversity. Invited Review.
Ko, K., Taylor, D., Argenton, P., Innes, J.,
Pedram, B., Siebert, F., Granell,
A, Ko, Z. 2005. Evidence that the
plastid translocon Tic40 components possess modulating capabilities. J.
Biol. Chem. 280: 215-224.
Labate, M.T.V., Ko, K., Ko,
Z.W., Costa Pinto, L.S.R., Real, M.J.U.D., Romano, M.R., Barja,
P.R., Granell, A., Friso,
G., van Wijk, K.J., Brugnoli,
E., Augusti, A., Labate,
C.A. 2004. Constitutive expression of pea Lhcb1-2 in tobacco affects plant
development, morphology and photosynthetic capacity. Plant Mol. Biol. 55:
702-714.
Ko, K.,
Banerjee, S., Innes, J., Taylor, D., Ko, Z. 2004. The Tic40 translocon components exhibit preferential interactions
with different forms of the Oee1 plastid protein precursor. Functional Plant
Biol. 31: 285-294.
Taylor, D., Bedard, J., Ko, K. 2004. A
cross-organelle proteomic approach for elucidating plastid translocon function.
Proceedings of the XIIth International Congress:
Genes, Gene Families, and Isozymes. CD-ROM
Publication January 2004. Pages 93-97.
Ko, K., Banerjee, S., Innes, J., Granell, A.,
Gordon, B., Ko,
K. 2002. The plastid protein import machinery component Toc36 exhibits an
affinity for the bacterial protein translocation process. Arch. Biochem. Biophys. 404:147-157.
Leary, S.C., Lyons, C.N., Carlson, C.G., Kraft, C.S.,
Hill, B.C., Ko, K., Glerum,
D.M., Moyes, C.D. 2002. Chronic treatment with azide in situ leads to an irreversible loss of cytochrome c oxidase activity via
holoenzyme dissociation. J. Biol. Chem. 277:
11321-11328.
Cameron, B.A., Gilmour, K., Forster, R., Ko, K., Tufts, B. 2000. Unique distribution of the anion exchange protein in the sea
lamprey, Petromyzon marinus.
J. Comp. Physiol. B. 170:497-504.
Ko, K., Ko, Z. 1999. In vitro targeting of
the Toc36 component of the chloroplast envelope protein import apparatus
involves a complex set of signals. Biochim. Biophys. Acta. 1421: 198-206.
Pang, P., Meathrel, K., Ko., K.
1997. A component of the chloroplast protein import apparatus functions in
bacteria. J. Biol. Chem. 272: 25623-25627.
Kourtz, L., K. Ko.
1997. The early stage of chloroplast protein import involves Com70.
J. Biol. Chem. 272: 2808-2813.
Schnell, D.J., Blobel, G., Keegstra, K., Kessler, F., Ko, K., Soll, J. 1997.
Nomenclature for the protein import components of the chloroplast envelope.
Trends in Cell Biol. 7:303-304
Wan, J., S. Blakeley, D.T. Dennis, K. Ko. 1996. Transit
peptides play a major role in the preferential import of proteins into
chloroplasts and leucoplasts. J. Biol. Chem. 271: 31227-31233.
Ko, K., D. Budd, C. Wu, F. Seibert, L. Kourtz,
Z.W. Ko. 1995. Isolation and
characterization of a cDNA clone encoding a member of
the Com44/Cim44 envelope components of the chloroplast protein import
apparatus. J. Biol. Chem. 270: 28601-28608.
Wan, J., S. Blakeley, D.T. Dennis, K.Ko. 1995. Import characteristics of a
leucoplast pyruvate kinase
are influenced by a 19 amino acid domain within the protein. J. Biol.
Chem. 270: 16731-16739.
Wu, C., F. Seibert, K.Ko.
1994. Identification of chloroplast envelope proteins in close physical
proximity to a partially translocated chimeric precursor protein. J. Biol. Chem. 269:
32264-32271.
Wu, C., K. Ko.
1993. Identification of an uncleavable
targeting signal in the 70-kilodalton spinach chloroplast outer envelope membrane
protein. J. Biol. Chem. 268: 19384-19391.
Ko, K., O. Bornemisza, L. Kourtz, Z.W. Ko,
W.C. Plaxton and A.R. Cashmore.
1992. Isolation and characterization of a cDNA
clone for a cognate 70 kDa heat shock protein
associated with the chloroplast envelope. J. Biol. Chem.
267:2986-2993.
Ko, K., Z.W. Ko. 1992. Carboxyl-terminal
sequences can influence the In vitro import and intra-organellar targeting of
chloroplast protein precursors. J. Biol. Chem. 267:13910-13916.
Ko, K., and A.R. Cashmore. 1989. Targeting
of proteins to the thylakoid lumen by the bipartite
transit peptide of the 33 kD
oxygen-evolving protein. EMBO J. 8:3187-3194.