A Plasma Membrane-associated Protein of Arabidopsis thaliana AtPCaP1 Binds Copper Ions and Changes Its Higher Order Structure

Abstract

PCaP1, a hydrophilic cation-binding protein, is bound to the plasma membrane in Arabidopsis thaliana. We focused on the physicochemical properties of PCaP1 to understand its uniqueness in terms of structure and binding of metal ions. On fluorescence analysis, PCaP1 showed a signal of structural change in the presence of Cu(2+). The near-UV CD spectra showed a marked change of PCaP1 in CuCl(2) solution. The far-UV CD spectra showed the presence of alpha-helices and the intrinsically unstructured region. However, addition of Cu(2+) gave no change in the far-UV CD spectra. These results indicate that Cu(2+) induced a change in the tertiary structure without changing the secondary structure. The protein was sensitive to proteinase in the presence of Cu(2+), supporting that Cu(2+) is involved in the structural change. The PCaP1 solution was titrated with CuCl(2) and the change in the fluorescence spectrum was monitored to characterize Cu(2+)-binding properties. The obtained values of K(d) for Cu(2+) and the ligand-binding number were 10 microM and six ions per molecule, respectively. These findings indicate that PCaP1 has a high Cu(2+)-binding capacity with a relatively high affinity. PCaP1 lacks cysteine and histidine residues. A large number of glutamate residues may be involved in the Cu(2+) binding.

Comparative proteomic analysis reveals similar and distinct features of proteins in dry and wet stigmas

“…For instance, the presence of the peroxidase and APG proteins described above may reflect the receptive state of the stigma to receive pollen grains. The DREPP plasma membrane polypeptide and Jacalin‐like lectin domain containing protein were previously hypothesized to be involved in inter‐ or intracellular signal transduction in the stigma [].…”

A novel-type phosphatidylinositol phosphate-interactive, Ca-binding protein PCaP1 in Arabidopsis thaliana: stable association with plasma membrane and partial involvement in stomata closure

“…4). The N-myristoylation and the N-terminal lysine-rich region might be essential for stable association of the protein to the membrane as suggested by in vitro analyses (Nagasaki-Takeuchi et al 2008). In addition to the N-myristoylation, the N-terminal polybasic cluster may be key properties for interaction of the region with the negatively charged PtdInsPs (McLaughlin and Murray 2005).…”

“…Increase in PCaP1 transcription by excessive copper was reported previously (Ide et al 2007). Furthermore, PCaP1 has been reported to bind Cu 2+ and change its higher order structure (Nagasaki-Takeuchi et al 2008). To examine effect of copper on the expression of PCaP1, seeds of plant expressing PCaP1 pro ::PCaP1-GFP were germinated and grown under excessive copper conditions at 0.1 mM CuSO 4 .…”

“…Thus, the enhancement of PCaP1 accumulation by Cu 2+ might be independent of the elicitor effect and related to biochemical characteristics of PCaP1. PCaP1 protein has a capacity to bind Cu 2+ ions in vitro experiments (Nagasaki-Takeuchi et al 2008). Thus, the enhancement of PCaP1 might be a reaction for adaptation and tolerance to excessive Cu 2+ .…”

PCaPs, possible regulators of PtdInsP signals on plasma membrane

“…It should be noted that PCaP1 has an intrinsically disordered region in the central and C-terminal parts. 5 The intrinsically disordered (ID) protein is defined to possess a relatively long sequence of more than 50 amino acid residues that is intrinsically disordered or has no folded structure. Most ID proteins are rich in glutamate, lysine, proline, serine or glutamine residues.…”