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 | Annexin 24(Ca32)
Capsicum annuum
PDB: 1dk5
The structure of Anx24 from bell pepper was the first structure of any plant annexins to be solved. Hydrophobic and basic residues on the convex (membrane-binding) side of the protein are responsible for a second, calcium-independent membrane binding mode which seems to be a characteristic feature of several plant annexins that distinguishes them from their vertebrate relatives. |
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Annexin A3:BDA452, Annexin A5:BDA452
Homo sapiens
Human annexins A3 and A5 were complexed within the crystals with BDA452, a new 1,4-benzodiazepine derivative. BDA452 binds to a cleft which is located close to the N-terminus opposite to the membrane binding side of the proteins. Biophysical studies of the interactions of various benzodiazepine derivatives with annexins were performed to analyse the binding of benzodiazepines to annexins and their effects on the annexin-induced calcium influx into phospholipids vesicles. Benzodiazepines modulate the membrane effects of annexins allosterically. |  |
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 | Annexin A6
Homo sapiens
The crystal structure of calcium-free recombinant human annexin VI shows two similar halves closely resembling annexin I connected by an -helical segment and arranged perpendicular to each other. The calcium and membrane binding sites assigned by structural homology are therefore not located in the same plane. Analysis of the membrane-bound form of annexin VI by electron microscopy shows the two halves of the molecule coplanar with the membrane, but oriented differently to the crystal structure and suggesting a flexible arrangement (see also structure by Kretsinger's group: PDF). |
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Annexin Gh1
Gossypium hirsutum
PDB: 1n00
The structure indicates that canonical calcium binding is geometrically possible within the membrane loops in domains I and II. The tryptophan residue in the IAB loop, which is highly conserved in plant annexins, is in a surface-exposed position, half way between both conformations observed in Anx24(Ca32). An unusual sulphur cluster formed by two cysteines and a methionine in domains II and III with S-S distances of about 5 Å might form the molecular basis for annexin function in oxidative stress response. |  |
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 | Calcium-bound annexin Gh1
Gossypium hirsutum
PDB: 3brx
Plant annexins show distinct differences when compared to their animal orthologues. In particular, the endonexin sequence, which is responsible for coordination of calcium ions in type II binding sites, is only partially conserved in plant annexins.
The crystal structure of calcium-bound cotton annexin Gh1 was solved at 2.5 Å resolution, and shows three metal ions coordinated in the first and fourth repeat in type II and III binding sites. While the protein has no detectable affinity for calcium in solution in the presence of phospholipid vesicles, we determined a stoichiometry of four calcium ions per protein molecule using isothermal titration calorimetry. Further analysis of the crystal structure shows that binding of a fourth calcium ion is structurally possible in the DE loop of the first repeat. Data from this study are in agreement with the canonical membrane-binding of annexins which is facilitated by the convex surface associating with the phospholipid bilayer by a calcium bridging mechanism. In annexin Gh1, this membrane-binding state is characterised by four calcium bridges in the I/IV module of the protein, and direct interactions of several surface-exposed basic and hydrophobic residues with the phospholipid membrane. |
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Carbonic Anhydrase II in complex with anomeric sulfonamides/sulfamates
Homo sapiens
PDB: 3hkn,3hkq,3hkt,3hku
A new class of carbonic anhydrase (CA) inhibitor was designed to selectively target the extracellular domains of the cancer-relevant CA isozymes. The aromatic moiety of the classical zinc binding sulfonamide CA inhibitors is absent from these compounds and instead they incorporate a hydrophilic mono- or disaccharide fragment directly attached to the sulfonamide group to give S-glycosyl primary sulfonamides. We solved the crystal structures of three anomeric sulfonamides and the sugar sulfamate drug topiramate in complex with human recombinant CA II. From these structures we have obtained valuable insights into ligand-protein interactions of these novel carbohydrate-based sulfonamides with CA. |  |
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 | Cyclase-associated Protein (CAP), N-terminal domain
Dictyostelium discoideum
PDB: 1tjf
CAP is a highly conserved and widely distributed protein that links the nutritional response signalling to cytoskeleton remodelling. We solved the orthorhombic crystal structure of the N-terminal domain of CAP that occurred due to auto-proteolytic cleavage in preparations using the full-length protein. Comparison with other CAP structures reveals variable modes of dimerisation of this domain, but the presence of a common interface for the side-to-side dimer. |
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cyclic Green Fluorescent Protein
Aequorea victoria
PDB: 1kp5
Crystals of cyclic green fluorescent protein (cGFP) engineered by the split intein technology in the group of A Plückthun were obtained and the structure was solved using molecular replacement. Although the core of the protein can unambiguously be fitted from the first to the last residue of the genuine sequence, the electron density in the region of the linker peptide is rather poor owing to the high water content of the crystals. Therefore, it is concluded that this part of the protein is highly disordered in the present structure and is very flexible. Nevertheless, the density is consistent with the loop being intact, as confirmed by mass spectroscopy of dissolved crystals. This structure contains an antiparallel cGFP dimer where the dimer interface is clearly different from other crystal structures featuring two GFP molecules. The cylinder surface of GFP is rather versatile and can employ various polar and non-polar patches in protein-protein interactions. |  |
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 | Cyclic nucleotide phosphodiesterase
Arabidopsis thaliana
PDB: 1fsi,1jh6,1jh7
The oxidised structure of cyclic nucleotide phosphodiesterase (CPDase) from Arabidopsis thaliana was the first one to be solved for any member of this family of 2H phosphodiesterases. The name stems from the signature tandem motif constituted by two H-X-T/S-X sequences.
CPDase possesses six cysteine residues, four of which are involved in forming two intra-molecular disulfide bridges. One of these bridges, between Cys-104 and Cys-110, is opened in the semireduced CPDase, whereas the other remains intact. This change of the redox state leads to a conformational rearrangement in the loop covering the active site of the protein. While the native structure shows this partially disordered loop in a coil conformation, in the semireduced enzyme the N-terminal lobe of this loop winds up and elongates the preceding alpha-helix. The semireduced state of CPDase also enabled co-crystallization with a putative inhibitor of its enzymatic activity, 2',3'-cyclic uridine vanadate.
The main target of this plant protein is ADP-ribose 1'',2''-cyclic phosphate, a product of the tRNA splicing reaction. |
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Ferredoxin-NADP+ reductase
Capsicum annuum
PDB: 1sm4
The first crystals of this protein were obtained accidentally during our efforts to crystallise native
annexin 24(Ca32) purified from bell pepper. Subsequently, the cDNA of this protein was prepared, and
the complete gene encoding paprika ferredoxin-NADP(+) reductase (pFNR) precursor was sequenced and cloned.
The overall structure of pFNR is similar to other members of the ferredoxin-NADP(+) reductase family, the
major differences concern a long loop that forms part of the FAD binding site and some
of the variable loops in surface regions. |  |
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 | Interactions of Visinin-like Proteins with phospho-inositides
The subcellular membrane localization of neuronal calcium sensor proteins in living cells, such as Visinin-like Proteins-1 (VILIP-1) and VILIP-3, differs substantially. We have followed the hypothesis that the differential localization may be due to the specific binding capabilities of individual VILIPs for phosphatidylinositol phosphates. Several highly conserved lysine residues in the N-terminal region could provide favourable electrostatic interactions. Molecular modelling results support a binding site for phospho-inositides in the N-terminal area of VILIP-1, and the involvement of the conserved N-terminal lysine residues in binding the phospho-inositol head group.
(Cover illustration of Aust. J. Chem. 2010, 63) |
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Natural product based phenols in complex with carbonic anhydrase II
Homo sapiens
PDB: 3nb5
A library of natural products and their synthetic derivatives has been investigated for enzyme inhibition against carbonic anhydrases (CAs), comprising the two human alpha-family CAs I and II and two Mycobacterium tuberculosis beta-family CAs. In support of this study, the structures of several compounds from this library were determined in their enzyme-boudn forms, using human CAII. |  |
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