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Abstract Detail


Protein Modification and Turnover

Dirk, Lynnette M.A. [1], Houtz, Robert L. [2].

Isolation and characterization of Rubisco small subunit αN-methyltransferase.

In many proteins, including the small subunit (SS) of Rubisco, the α-amino group on the N-terminal amino acid residue is methylated. Some studies have suggested that a unique class of protein methyltransferase may catalyze this modification. Earlier studies from this laboratory associated methylation of the N-terminal Met residue in the processed form of the Rubisco SS with the same SET-domain protein methyltransferase responsible for methylation of Lys-14 in the large subunit (LS) of Rubisco. However, recent analyses of transgenic tobacco plants with reduced amounts of Rubisco LSMT were not accompanied by altered methylation at Met-1 in the SS. To clarify the relationship, or lack thereof, between methylation at Lys-14 in the LS and Met-1 in the SS, we have partially purified the Rubisco SS methyltransferase from spinach. The enzyme, estimated as a 60 kDa polypeptide, was purified approximately 150-fold to a specific activity of ~14.3 nmoles of methyl groups transferred per min per mg protein using isolated spinach chloroplasts as starting material and was assayed using a guanidine-HCl-denatured form of the SS. However, denatured small subunit was susceptible to a time dependent inactivation as a substrate for Rubisco SS methyltransferase due to the formation of an internal disulfide bond as evident by a 2 dalton molecular mass shift in the SS. Trypsinolysis and peptide mass-spectrometric analyses will be performed on candidate proteins to identify potential orthologues from protein databases.


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1 - University of Kentucky, Horticulture; Plant Physiology/Biochemistry/Molecular Biology Program, 441 Plant Science Building, 1405 Veterans Drive, Lexington, Kentucky, 40546-0312, USA
2 - University of Kentucky, Horticulture; Plant Physiology/Biochemistry/Molecular Biology Program

Keywords:
methylation
rubisco
Rubisco Large Subunit Methyl Transferase
small subunit.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P37015
Abstract ID:2147


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