Our major goal is to understand how the pathway of protein import into chloroplasts is regulated, and elucidate the key components involved and their functional roles. The chloroplast carries out the essential reactions of photosynthesis, and houses an amazing array of biosynthetic pathways required for plant development. The chloroplast contains its own DNA, but ~98% of its proteins are encoded by the nuclear genome and synthesized in the cytosol as precursors that must be imported. We identified a zinc-binding stromal processing peptidase (SPP) that removes targeting signals from nearly all proteins entering the chloroplast, allowing them to achieve their functional conformations. Biochemical and transgenic plant studies demonstrated that SPP has been highly conserved during evolution and is essential for plant survival. Because of its pivotal role during protein import, we are establishing how SPP recognizes its unique precursor substrates, the mechanism underlying cleavage, and how SPP activation is controlled.
To broaden our understanding of the chloroplast import pathway, we developed a novel genetic screen in the model plant Arabidopsis. An important class of mutants revealed that the regulation of protein import is integrated into a nitrogen-dependent metabolic network linked to purine catabolism. Chloroplast development and adaptation to light and abiotic stress are altered in the mutants. These findings have important implications for the timing of leaf senescence and plant productivity that depend on efficient photosynthesis and chloroplast metabolism. Our genetic screen provides a new perspective to identify the decisive factors that regulate chloroplast protein import amid a dynamic, and often challenging, cellular environment.
Lamppa, G. and Zhong, R. 2013. Chloroplast stromal processing peptidase. IN: Handbook of Proteolytic Enzymes. Third edition. Eds. N. Rawlings and G. Salvese, Elsevier Ltd, London. Invited review chapter, pp. 1442-1447.
Zhong, R. Thomspon, J., Otttesen, E., and Lamppa, G. 2010. A forward genetic screen to explore chloroplast protein import in vivo identifies Moco sulfurase, pivotal for ABA and IAA biosynthesis and purine turnover. Plant J. 63: 44-59. (PubMed)
Ottesen, E., Zhong, R., and Lamppa, G. 2010. Identification of a chloroplast division mutant coding for ARC6H, an ARC6 homolog that plays a nonredundant role. Plant Science 178: 114-122. (ScienceDirect)
Ponpuak, M., Klemba, M., Park, M.,
Gluzman, I., Lamppa, G. and Goldberg, D. 2007. A role for falcilysin
in transit peptide degradation in the Plasmodium falciparum apicoplast.
Molecular Microbiol.: 63: 314-334. (PubMed)
Richter, S., Zhong, R. and Lamppa,
G. (2005) Function of the stromal processing peptidase in the chloroplast
import pathway. (Review) Physiol. Plant. 123: 362-368.
Rudhe, C., Clifton, R., Chew, O.,
Zeman, K., Richter, R., Lamppa, G., Whelan, J., and
Glaser, E. 2004. Processing of the dual targeted precursor protein
of glutathione reductase in mitochondria and chloroplasts. J. Mol.
Biol. 343: 639-647. (PubMed)
Jin, R., Richter, S., Zhong, R. and
Lamppa, G. K. (2003). "Expression and import of an active cellulase
from a thermophilic bacterium into the chloroplast both in vitro
and in vivo." Plant Mol Biol 51: 493-507. (PubMed)
Zhong, R., Wan, J., Jin, R. and Lamppa,
G. (2003). "A pea antisense gene for the chloroplast stromal
processing peptidase yields seedling lethals in Arabidopsis: survivors
show defective GFP import in vivo." Plant J 34: 802-12. (PubMed)
Richter, S. and Lamppa, G. K. (2003).
"Structural properties of the chloroplast stromal processing
peptidase required for its function in transit peptide removal."
J Biol Chem 278: 39497-502. (PubMed)
Richter, S. and Lamppa, G. K. (2002).
"Determinants for removal and degradation of transit peptides
of chloroplast precursor proteins." J Biol Chem 277: 43888-94.