In this study, the domain movement of AnxAl in response to Ca<sup>2+</sup> in the presence of phospholipid membrane was studied using the intrinsic fluorophore Tryptophan 12 on its N-terminal domain. Increases in fluorescence intensity and blue shift of emission peak wavelength show that the N-terminal domain has a hydrophobic interaction with phospholipids. Neutron diffraction profiles of multi-stack phospholipid bilayers in the presence of AnxAl N-terminal peptides indicate that the peptides lie parallel to the surface of phospholipid bilayers. These results support the notion that the N-terminal domain interacts with membranes in a calcium-independent manner. A model where membrane aggregation is mediated simultaneously by the two membrane binding sites of one AnxAl molecule is thus possible. Plant annexins, annexin Ghl from <i>Gossypium hirsutum </i>and annexin 24 from <i>Capsicum annuum </i>(Anx(Ghl) and Anx24(Ca32), respectively), have been reported to possess a calcium-dependent membrane binding behaviour similar to animal annexins. Interestingly, hydrophobic and positively charged residues are well conserved among plant annexins, and fully exposed on the convex side (canonical membrane binding side) of the C-terminal core surface. In this study, AnxAl(Gh1) and Anx24(Ca32) are demonstrated to also possess calcium-independent membrane binding activity, which is directly attributed to these conserved surface residues. Anx(Gh1) was successfully crystallised using high concentration of CaCl<sub>2</sub> in a phosphate crystallisation buffer. Three Ca<sup>2+</sup> ions are localised in the Ca<sup>2+</sup>-bound structure presenting typical Ca<sup>2+</sup> coordination geometries observed in animal annexins. Two adjacent cysteine residues, Cys116 and Cys243, have been speculated to carry a putative RedOx function of Anx(Ghl). The RedOx activity of Cys116 and Cys243 was probed using trypsin digest mapping of Anx(Ghl) with H<sub>2</sub>O<sub>2</sub> treatment. These experiments indicate that the two cysteine residues remain a reduced state.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652668 |
| Date | January 2007 |
| Creators | Hu, Nien-Jen |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14121 |
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