Gayle K Lamppa

Organelle biogenesis in eucaryotes depends on the import of nuclear-encoded proteins from the cytosol. The chloroplast, the photosynthetic organelle in plants, imports at least 90% of its proteins, which are typically synthesized as precursors with an N-terminal extension, a transit peptide, that mediates multiple steps as proteins are targeted to the correct organelle, cross a defining membrane, and undergo proteolytically processing to reach their mature, functional form. We have identified a general stromal processing peptidase, SPP, responsible for transit peptide removal, a critical step in the import pathway. SPP is a member of a metallopeptidase family that depends on a zinc-binding motif for its activity. Our studies have explored the specificity of the protein-protein interactions that occur as SPP recognizes and cleaves the transit peptide. Downregulation of SPP in transgenic Arabidopsis yields many seedling lethals, demonstrating that SPP is encoded by an essential gene. Low levels of SPP severely affect other steps in the import pathway, as demonstrated by following the fate of green fluorescent protein (GFP) fused to a transit peptide in the same transgenic plants. Based on the GFP results, we have developed a genetic screen to identify chloroplast import mutants that depends both on the correct import of GFP and a chloroplast enzyme that confers herbicide resistance. We have identified novel mutants that should provide important insights into how proteins are selectively targeted to chloroplasts and the components that regulate this complex pathway during organelle biogenesis.

Organelle biogenesis in eucaryotes depends on the import of nuclear-encoded proteins from the cytosol. The chloroplast, the photosynthetic organelle in plants, imports at least 90% of its proteins, which are typically synthesized as precursors with an N-terminal extension, a transit peptide, that mediates multiple steps as proteins are targeted to the correct organelle, cross a defining membrane, and undergo proteolytically processing to reach their mature, functional form. We have identified a general stromal processing peptidase, SPP, responsible for transit peptide removal, a critical step in the import pathway. SPP is a member of a metallopeptidase family that depends on a zinc-binding motif for its activity. Our studies have explored the specificity of the protein-protein interactions that occur as SPP recognizes and cleaves the transit peptide. Downregulation of SPP in transgenic Arabidopsis yields many seedling lethals, demonstrating that SPP is encoded by an essential gene. Low levels of SPP severely affect other steps in the import pathway, as demonstrated by following the fate of green fluorescent protein (GFP) fused to a transit peptide in the same transgenic plants. Based on the GFP results, we have developed a genetic screen to identify chloroplast import mutants that depends both on the correct import of GFP...

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. 

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 Citation

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 Citation

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 Citation

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.   PubMed Citation

Richter, S. and Lamppa, G. K. (1999). "Stromal processing peptidase binds transit peptides and initiates their ATP-dependent turnover in chloroplasts." J Cell Biol 147: 33-44.   PubMed Citation

Richter, S. and Lamppa, G. K. (1998). "A chloroplast processing enzyme functions as the general stromal processing peptidase." Proc Natl Acad Sci U S A 95: 7463-8.   PubMed Citation

Wan, J., Bringloe, D. and Lamppa, G. (1998). "Disruption of chloroplast biogenesis and plant development upon downregulation of a chloroplast processing enzyme involved in the import pathway." Plant J. 15: 459-468.  

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. 

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 Citation

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 Citation

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 Citation

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.   PubMed Citation