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Publication Abstract from PubMed

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 Mg(2+) , or 100 muM Ca(2+) . 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 Mg(2+) , the divalent ion is bound by EF-hand 2, perturbing interhelical angles and imposing more regular helical structure. The structure of Ca(2+) -bound Phl p 7 resembles that previously reported for Bet v 4-likewise exposing apolar surface to the solvent. Occluded in the apo- and Mg(2+) -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 Ca(2+) . When Mg(2+) resides in site 2, the D55 carboxylate withdraws to a distance consistent with a role as an outer-sphere ligand. (15) N relaxation data, collected at 600 MHz, indicate that backbone mobility is limited in all three ligation states. Proteins 2013. (c) 2012 Wiley Periodicals, Inc.

Solution structures of polcalcin Phl p 7 in three ligation states: Apo-, hemi-Mg(2+) -bound, and fully Ca(2+) -bound.,Henzl MT, Sirianni AG, Wycoff WG, Tan A, Tanner JJ Proteins. 2013 Feb;81(2):300-15. doi: 10.1002/prot.24186. Epub 2012 Nov 12. PMID:23011803^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.