STRUCTURAL BASIS OF NUCLEIC ACID RECOGNITION BY THE N-TERMINAL COLD SHOCK DOMAIN OF THE PLANT GLYCINE-RICH PROTEIN AtGRP2

AtGRP2 is a glycine-rich, RNA-binding protein that plays pivotal roles in abiotic stress response and flowering time regulation in Arabidopsis thaliana. AtGRP2 consists of an N-terminal cold shock domain (CSD) and two C-terminal CCHC-type zinc knuckles interspersed with glycine-rich regions. The objective of this work was to investigate thestructure, dynamics, and nucleic acid binding properties of AtGRP2-CSD. The 2D [1H,15N] HSQC spectrum of AtGRP2-CSD1-79 revealed the presence of an unfolded state in equilibrium with the folded state. The addition of eleven residues at the C-terminus stabilized the folded conformation. The three-dimensional structure of AtGRP2-CSD1-90 unveiled a β-barrel composed of five antiparallel β-strands with anordered C-terminal extension, a conserved feature in eukaryotic CSDs. Direct contacts between the C-terminal extension and the β3-β4 loop further stabilized the CSD fold. AtGRP2-CSD1-90 exhibited nucleic acid binding via solvent-exposed residues on strands β2 and β3, as well as the β3-β4 loop, with higher affinity for DNA over RNA, particularly favoring pyrimidine-rich sequences. Furthermore, DNA binding induced rigidity in the β3-β4 loop, evidenced by 15N-{1H} NOE values, and increased the R2/R1 ratio for residues in the binding interface. Mutation of residues W14, F26, and F37, in the central β-sheet, completely abolished DNA binding, highlighting the significance of π-stacking interactions in the binding mechanism. These results shed light on the mechanism of nucleic acid recognition employed by AtGRP2, creating a framework for the development of biotechnological strategies aimed at enhancing plant resistance toabiotic stresses.
 

This work was supported by Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), and Conselho Nacional Científico eTecnológico (CNPq).