Abstract
We investigated the structural and dynamic characters of two proteins in the study: Hepatoma-derived growth factor (HDGF) and receiver domain of ethylene receptor 1 (ETR1-RD). In the first case, HDGF-related proteins (HRPs) contain conserved N-terminal HATH domains with a characteristic PWWP motif. The HATH domains have drawn attention because of the binding with heparin/heparan sulfate, DNA and methylated histone peptide. Depending on the sequence of the PWWP motif, HATHs are classified into P-type (Pro-His-Trp-Pro) and A-type (Ala-His-Trp-Pro). A-type HATH is highly unstable in solution and P-type HATH has available structure. We evaluated the difference on structure, dynamics and ligand binding. Analysis of NMR backbone 15N relaxations revealed additional backbone dynamics in the interface between the b-barrel and the C-terminal helix bundle. The β1/β2 loop, where the AHWP sequence is located, has great structural flexibility, which aids HATH-HATH interaction. A-type HATH, therefore, shows a tendency toward higher-order aggregation when binding with heparin and DNA oligomers. In the second case, ETR1, in response to ethylene, plays versatile roles in plant physiology. Although the downstream regulators have been identified, the molecular recognition remains unknown. It has been speculated that the cytoplasmic signaling of ETR1 adopts a two-component system involving the conserved receiver domain (RD). We used NMR method to investigate the structure and dynamics of ETR1-RD. Combining NMR backbone chemical shifts into the structural calculation, we defined the solution ETR1-RD structure similar to X-ray structure, but ETR1-RD is a monomer, not the dimer observed in X-ray crystal. Notably, NMR investigation reported no phosphorylation for ETR1-RD. Comparing the backbone dynamics to other receiver regulators, we suspect the backbone flexibility is critical to determine the phosphorylation property. ETR1-RD is an atypical receiver regulator.