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Dr.
Hanjo Hellmann
.jpg) 509-335-2762
hellmann@wsu.edu
Assistant Professor, School of Biological Sciences. Ph.D.
1997, Ph.D., Eberhardt-Karls-University Tübingen, Germany.
Research
In
plants and most eukaryotes, the ubiquitin proteasome pathway
has been proven to be crucial for many developmental and regulatory
processes. The pathway is a response mediator of various different
signals which are perceived by cellular receptors and transduced
within the cell. E3 ubiquitin ligases are the key players in
this pathway and facilitate transfer of the ubiquitin moiety
to substrate proteins, which are usually transcription factors,
thereby controlling stability and activity of these proteins
and their downstream target genes. Cullin proteins are a common
core subunit of many E3 ligase complexes. My group’s main
interest is in E3 ligases that contain cullins which have been
demonstrated to participate in such important processes as embryo
and organ development, phytohormone signal transduction, stress
tolerance and light response.
Ongoing goals in the group are:
(1) to unravel cellular and environmental
conditions like phytohormones, heat stress, or light that lead
to assembly of the different cullin based complexes within the
cell,
(2) to characterize organ and cell specific
responses,
(3) to identify substrate proteins that
are degraded or modified by these E3 ligases,
(4) to characterize signal
transduction pathways activating the different cullin-based E3
ligases and
(5) to functionally describe gain- and loss-of-function
mutants affected in E3 ligase subunits or
substrate proteins.
Vitamin
B6, or pyridoxine, is an important compound that mediates more than
100 biochemical reactions. Plants, fungi, and some bacteria can synthesize
this vitamin, however in humans and other mammals it must be taken
up from nutrients. Several important functions of this vitamin include
alleviating oxidative stress in fungus and UV-light and salt stress
in higher plants. My group is interested in the final steps of vitamin
B6 biosynthesis, which are catalyzed by two small protein families
that assemble to higher-order protein complexes. Specifically, what
mechanisms control activity of the protein complexes and how is this
activity connected with stress tolerance in higher plants.
Undergraduate students: Interested
students are always welcome to do internships or BIO499 classes
on selected topics to gain practical experiences in laboratory
work.
Graduate students: I am currently accepting graduate
students. Please feel free to contact me if you are interested
in joining the lab.
Selected
Publications
Leuendorf,
J.E., Genau, A., Szewczyk, A, Mooney, S., Drewke, C., Leistner,
E., Hellmann, H. 2007. The PDX1 family is structurally and functionally
conserved between Arabidopsis thaliana and Ginkgo
biloba. FEBS
J. 275, 960-969.
Weber, H.,
Hano, P., Hellmann, H. 2007. The Charming Complexity of Cul3.
Internat. J. Dev. Plant. 1:178-184.
Bernhardt,
A., Lechner, E., Hano, P., Schade, V., Dieterle, M., Anders,
M., Dubin, M.J., Benvenuto, G., Bowler, C., Genschik, P., Hellmann,
H. 2006. CUL4 associates with DDB1a and DET1 and its down
regulation affects diverse aspects of development in Arabidopsis
thaliana. Plant J. 47:591-603.
Wagner, S.,
Bernhardt, A., Leuendorf, J.E., Drewke, C., Lytovchenko, A.,
Mujahed, N., Gurgui, C., Frommer, W.B., Leistner, E., Fernie,
A.R., Hellmann, H. 2006. Analysis of the Arabidopsis rsr4-1/pdx1-3
Mutant Reveals the Critical Function of the PDX1 Protein Family
in Metabolism, Development, and Vitamin B6 Biosynthesis. Plant
Cell. 18:1722-1735.
Weber, H.,
Bernhardt, A., Dieterle, M., Hano, P., Mutlu, A., Estelle, M.,
Genschik, P., Hellmann, H. 2005. Arabidopsis AtCUL3a and AtCUL3b
form complexes with members of the BTB/POZ-MATH protein family.
Plant Physiol. 137, 83-93.
Ren,
C., Pan, J., Peng, W., Genschik, P., Hobbie, L., Hellmann, H.,
Estelle, M., Gao, B., Peng, J., Sun, C., Xie, D. 2005. Point mutations
in Arabidopsis Cullin1 reveal its essential role in jasmonate
response Plant J. 42:514–524.
Figueroa,
P., Gusmaroli, G., Serino, G., Habashi, J., Ma, L., Shen, Y.,
Feng, S., Bostick, M., Callis, J., Hellmann, H., Deng, X.W. 2005.
Arabidopsis has two redundant Cullin3 proteins that
are essential for embryo development and that interact with RBX1
and BTB proteins to form multisubunit E3 ubiquitin ligase complexes
in vivo. Plant Cell 17:1180-1195.
Gingerich,
D.J., Gagne, J.M., Salter, D.W., Hellmann, H., Estelle, M., Vierstra,
R.D. 2005. Cullin 3A and B assemble with members of the broad
complex/tramtrack/bric-A-brac (BTB). J Biol Chem. 280:18810-18821.
Hellmann,
H., Hobbie, L., Chapman, A., Dharmasiri, S., Dharmasiri, N.,
del Pozo, C., Reinhardt, D., Estelle, M. 2003. Arabidopsis AXR6
encodes CUL1 implicating SCF E3 ligases in auxin regulation of
embryogenesis. EMBO J. 22:3314-3325.
Dharmasiri
S., Dharmasiri N., Hellmann H., Estelle M. 2003. The RUB/Nedd8
conjugation pathway is required for early development in Arabidopsis.
EMBO J. 22:1762-1770.
Gray W.M.,
Hellmann H., Dharmasiri S., Estelle M. 2002. Role of the Arabidopsis RING-H2
protein RBX1 in RUB modification and SCF function. Plant Cell 14:2137-2144.
Hellmann,
H. and Estelle M. 2002. Plant development: regulation by protein
degradation. Science 297:793-797.
Shen W.H.,
Parmentier Y., Hellmann H., Lechner E., Dong A., Masson J., Granier
F., Lepiniec L., Estelle M., Genschik P. 2002. Null mutation
of AtCUL1 causes arrest in early embryogenesis in Arabidopsis.
Mol Biol Cell. 13:1916-1928.
del Pozo J.C.,
Dharmasiri S., Hellmann H., Walker L., Gray W.M., Estelle M.
2002. AXR1-ECR1-dependent conjugation of RUB1 to the Arabidopsis Cullin
AtCUL1 is required for auxin response. Plant Cell 14:421-433.
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