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Plant and Cell Physiology Advance Access published online on February 24, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcj021
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Plant and Cell Physiology 2006 © The Japanese Society of Plant Physiologists (JSPP); all rights reserved.
Received December 16, 2005
Accepted February 10, 2006

Regular Paper

Domain Swapping between a Cyanobacterial and a Plant Subunit ADP-Glucose Pyrophosphorylase

Alberto A. Iglesias 1, Miguel A. Ballicora 2 *, Juliana I. Sesma 3, and Jack Preiss 4

1 Laboratorio de Enzimología Molecular, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral. Paraje ‘El Pozo’, CC 242, S3000ZAA, Santa Fe, Argentina
2 Department of Chemistry, 405 Flanner Hall, 1068 W. Sheridan Rd., Lake Shore Campus, Loyola University at Chicago, Chicago, IL 60626 USA
3 Laboratorio de Enzimología Molecular, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral. Paraje ‘El Pozo’, CC 242, S3000ZAA, Santa Fe, Argentina; Current address: Instituto de Investigaciones Médicas M. y M. Ferreira (INIMEC), 5000 Córdoba, Argentina
4 Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA

* To whom correspondence should be addressed.
Miguel A. Ballicora, E-mail: mballic{at}luc.edu


  Abstract

ADP-glucose pyrophosphorylase (ADP-Glc PPase) catalyzes the regulatory step in the pathway for synthesis of bacterial glycogen and starch in plants. ADP-Glc PPases from cyanobacteria (homotetramer) and from potato (Solanum tuberosum) tuber (heterotetramer) are activated by 3-phosphoglycerate and inhibited by inorganic orthophosphate. To study the function of two putative domains, chimeric enzymes were constructed. PSSANA contained the N-terminus (292 amino acids) of the potato tuber ADP-Glc PPase small subunit (PSS) and the C-terminus (159 residues) of the Anabaena PCC 7120 enzyme. ANAPSS was the inverse chimeric. These constructs were expressed separately or together with the large subunit of the potato tuber ADP-Glc PPase (PLS), to obtain homo- and heterotetrameric chimeric proteins. Characterization of these forms showed that the N-terminus determines stability and regulatory redox-dependent properties. The chimeric forms exhibited intermediate 3-phosphoglycerate activation properties with respect to the wild-type homotetrameric enzymes indicating that the interaction between the putative N- and C-domains determine the affinity for the activator. Characterization of the chimeric heterotetramers showed the functionality of the large subunit, mainly in modulating regulation of the enzyme by the coordinate action of 3-phosphoglycerate and inorganic orthophosphate.

Keywords: ADP-glucose pyrophosphorylase; glycogen synthesis; starch synthesis; metabolic regulation; cyanobacteria; potato tuber.
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