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Chloroplast-Localized Co- and Post-Translational Processing Enzymes: Essential Determinants of Protein Maturation
Department of Horticulture
Co- and post-translational protein processing is often essential through influences on protein folding, stability, turnover, and activity. Additionally, it changes protein identity from that which can be deduced from DNA translation in unpredictable ways. Within the limited proteome of the chloroplast, a plethora of protein processing occurs, which, while recently physically characterized through newly developed techniques in mass spectroscopy polypeptide fingerprinting, have yet to be exploited through biochemical characterization of the associated enzymes, perhaps due to the inherent challenges therein.
The following studies capitalize on existing and previous accomplishments from the author's laboratory, widely recognized for discoveries in chloroplast-localized co- and post-translational protein processing. Application of these skills and abilities to the currently unknown areas of co- and post-translational processing enzymes in the chloroplast will provide information which allows prediction of protein processing and maturation in the chloroplast of all plants.
2009 Project Description
Collectively, co- and post-translational processing of proteins translated in the chloroplast form the final, biologically-active mature products from gene expression. Frequently these processes are unpredictable from protein primary sequence derived from DNA sequence, are often essential, and represent a collection of enzymes with evolved polypeptide substrate specificity and associated structural features that make them unique hybrids of their prokaryotic and eukaryotic counterparts.
Utilizing a collection of proven biochemical approaches and past accomplishments, this proposal provided structure/function relationships and in vivo functional significance for peptide deformylase (PDF), methionine aminopeptidase (MAP), and protein lysine methyltransferase (PKMT). Previous and existing biochemical and structural characterization of PDF and the PKMT, Rubisco LSMT, from this laboratory provided the rationale and justification for the approaches outlined in this proposal. Completion of the proposed studies provided unique structure/function relationships for co-and post-translational processing enzymes, and identification of polypeptide substrate specificity, and the mechanistic information that explains how they interact with all chloroplast-translated proteins.
The findings from these studies resulted in the development of new approaches for the control of weeds through the use of peptide deformylase inhibitors and the construction of transgenic plants resistant to those inhibitors. Others interested in chloroplast protein processing benefited from identification of the mechanism that determines the N-termini of chloroplast-translated proteins.
Whitney SM, Kane HJ, Houtz RL, & Sharwood RE (2009) Rubisco oligomers composed of linked small and large subunits assemble in tobacco plastids and have higher affinities for CO2 and O2. Plant Physiology,149(4):1887-1895.
Raunser, S., Magnani, R., Huang, Z., Houtz, R. L., Trievel, R. C., Penczek, P. A., and Walz, T. (2009). Rubisco in complex with Rubisco large subunit methyltransferase. PNAS , 106: 3160-3165.