Polcalcins are small EF-hand proteins believed to assist in regulating pollen-tube growth. Phl p 7, from timothy grass (Phleum pratense), crystallizes as a domain-swapped dimer at low pH. This study describes the solution structures of the recombinant protein in buffered saline at pH 6.0, containing either 5.0 mM EDTA, 5.0 mM Mg2+, or 100 μM Ca2+. Phl p 7 is monomeric in all three ligation states. In the apo-form, both EF-hand motifs reside in the closed conformation, with roughly antiparallel N- and C-terminal helical segments. In 5.0 mM Mg2+, the divalent ion is bound by EF-hand 2, perturbing interhelical angles and imposing more regular helical structure. The structure of Ca2+-bound Phl p 7 resembles that previously reported for Bet v 4—likewise exposing apolar surface to the solvent. Occluded in the apo- and Mg2+-bound forms, this surface presumably provides the docking site for Phl p 7 targets. Unlike Bet v 4, EF-hand 2 in Phl p 7 includes five potential anionic ligands, due to replacement of the consensus serine residue at –x (residue 55 in Phl p 7) with aspartate. In the Phl p 7 crystal structure, D55 functions as a helix cap for helix D. In solution, however, D55 apparently serves as a ligand to the bound Ca2+. When Mg2+ resides in site 2, the D55 carboxylate withdraws to a distance consistent with a role as an outer-sphere ligand. 15N relaxation data, collected at 600 MHz, indicate that backbone mobility is limited in all three ligation states. Proteins 2013. © 2012 Wiley Periodicals, Inc.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.