ABSTRACT
The enzyme glutamine synthetase (EC 6.3.1.2) is mainly responsible for the incorporation of inorganic nitrogen into organic molecules in plants. In the present work, a new pine GS1 (PpGS1b.2) gene was identified, showing a high sequence identity with the GS1b.1 gene previously characterized in conifers. Phylogenetic analysis revealed that the presence of PpGS1b.2 is restricted to the genera Pinus and Picea and is not found in other conifers. Gene expression data suggest a putative role of PpGS1b.2 in plant development, similar to other GS1b genes from angiosperms, suggesting evolutionary convergence. The characterization of GS1b.1 and GS1b.2 at the structural, physicochemical, and kinetic levels has shown differences even though they have high sequence homology. Alterations in the kinetic characteristics produced by the site-directed mutagenesis approach carried out in this work strongly suggest an implication of amino acids at positions 264 and 267 in the active center of pine GS1b.1 and GS1b.2. Therefore, the amino acid differences between GS1b.1 and GS1b.2 would support the functioning of both enzymes to meet distinct plant needs.
HIGHLIGHT A new GS1b paralog (GS1b.2) expressed in developing tissues has been identified in pine. The kinetic properties of the enzyme differ from those of the previously studied GS1b.1, despite their high sequence identity.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Authors e-mails: José Miguel Valderrama-Martín (jmvalderrama{at}uma.es); Francisco Ortigosa (fortigosa{at}uma.es); Juan Carlos Aledo (caledo{at}uma.es); Concepción Ávila (cavila{at}uma.es); Francisco M. Cánovas (canovas{at}uma.es); Rafael A. Cañas (rcanas{at}uma.es).
ABBREVIATIONS
- EC50
- the concentration of substrate that produces a half-maximal enzyme velocity
- Ki
- dissociation constant for substrate binding
- Km
- Michaelis-Menten constant
- nH
- Hill slope
- Vmax
- maximum enzyme velocity