Cloning and functional activity of a novel truncated form of annexin IV in mouse macrophages

Detection of human annexin A1 as the novel N-terminal tag for separation and purification handle

BACKGROUND

Several fusion tags for separation handle have been developed, but the fused tag for simply and cheaply separating the target protein is still lacking.

RESULTS

Separation conditions for the human annexin A1 (hanA1) tagged emerald green fluorescent protein (EmGFP) in Escherichia coli were optimized via precipitation with calcium chloride (CaCl₂) and resolubilization with ethylenediamine tetraacetic acid disodium salt (EDTA-Na₂). The HanA1-EmGFP absorbing with other three affinity matrix was detected, only it was strongly bound to heparin Sepharose. The separation efficiency of the HanA1-EmGFP was comparable with purification efficiency of the His6-tagged HanA1-EmGFP via metal ion affinity chromatography. Three fluorescent proteins for the EmGFP, mCherry red fluorescent protein and flavin-binding cyan-green fluorescent protein LOV from Chlamydomonas reinhardtii were used for naked-eye detection of the separation and purification processes, and two colored proteins including a red protein for a Vitreoscilla hemoglobin (Vhb), and a brown protein for maize sirohydrochlorin ferrochelatase (mSF) were used for visualizing the separation process. The added EDTA-Na₂ disrupted the Fe-S cluster in the mSF, but it showed little impact on heme in Vhb.

CONCLUSIONS

The selected five colored proteins were efficient for detecting the applicability of the highly selective hanA1 for fusion separation and purification handle. The fused hanA1 tag will be potentially used for simple and cheap affinity separation of the target proteins in industry and diagnosis.

Domain IV of Annexin A5 Is Critical for Binding Calcium and Guarantees Its Maximum Binding to the Phosphatidylserine Membrane

Background: Although domain IV of annexin A5 (anxA5) may be less effective in binding phosphatidylserine (PS), the four domains together may guarantee the maximum binding of anxA5 to the PS membrane. Additionally, previous research has shown that annexin mutants lacking one or more domain(s) have different biological activities compared to the wild-type. The present research mainly aims to study the role of domain IV in the crucial PS-binding function of anxA5. Methods: The domain IV-truncated anxA5 protein was constructed and purified. Isothermal titration calorimetry, flow cytometry and activated partial thromboplastin time were adopted to examine the function of domain IV in anxA5-PS binding directly or indirectly. Results: The domain IV-truncated form of anxA5 is impaired in binding PS liposome and apoptotic cells, and anticoagulation activity. The mutant cannot bind calcium, but binds PS only in the presence of calcium. Conclusions: Truncation of domain IV of anxA5 destroys its calcium-binding ability and impairs its PS-binding activity. Truncation of domain IV may induce conformation change of anxA5 or reduce the hydrophobic interactions between protein and membrane, which may explain the decrease of PS-binding affinity of the mutant.

Anxa4 Genes are Expressed in Distinct Organ Systems in Xenopus laevis and tropicalis But are Functionally Conserved

Anxa4 belongs to the multigenic annexin family of proteins which are characterized by their ability to interact with membranes in a calcium-dependent manner. Defined as a marker for polarized epithelial cells, Anxa4 is believed to be involved in many cellular processes but its functions in vivo are still poorly understood. Previously, we cloned Xanx4 in Xenopus laevis (now referred to as anxa4a) and demonstrated its role during organogenesis of the pronephros, providing the first evidence of a specific function for this protein during the development of a vertebrate. Here, we describe the strict conservation of protein sequence and functional domains of anxa4 during vertebrate evolution. We also identify the paralog of anxa4a, anxa4b and show its specific temporal and spatial expression pattern is different from anxa4a. We show that anxa4 orthologs in X. laevis and tropicalis display expression domains in different organ systems. Whilst the anxa4a gene is mainly expressed in the kidney, Xt anxa4 is expressed in the liver. Finally, we demonstrate Xt anxa4 and anxa4a can display conserved function during kidney organogenesis, despite the fact that Xt anxa4 transcripts are not expressed in this domain. This study highlights the divergence of expression of homologous genes during Xenopus evolution and raises the potential problems of using X. tropicalis promoters in X. laevis.

Annexin A4: A novel molecular marker for gastric cancer with Helicobacter pylori infection using proteomics approach

Helicobacter pylori was reported to be an important risk factor for the carcinogenesis of gastric cancer. Here, we used a proteomic approach to find differentially expressed proteins between the normal and tumor tissue of gastric cancer patients infected with H. pylori. In our results, we found annexin A4 was over-expressed in patients infected with H. pylori and was found in tumor cells, and over-expressed in gastric cancer SCM-1 cells after H. pylori infection. Ca(2+ ) can be induced by H. pylori and interact with annexin A4 Ca(2+) binding site to block the calmodulin-activated chloride conductance activation; therefore, it produces a new environment that benefits the malignant existence of H. pylori and raises the risk for gastric cancer. We also found interleuken-8 (IL-8) expression levels were increased in H. pylori infected SCM-1 cells. Combined with previous reports and our results, we summarize that the over-expression of annexin A4 in SCM-1 cells with H. pylori infection may subsequently induce IL-8 which can further cause tumor angiogenesis. In this paper, we show that annexin A4 is a potential novel molecular marker for gastric cancer with H. pylori infection, and our results may provide a new insight in the development of new anti-cancer drugs.

Intron disruption of the annexin IV gene reveals novel transcripts

Annexin IV (AIV), a Ca2+-dependent membrane-binding protein, is expressed in many epithelia. Annexin IV modifies membrane bilayers by increasing rigidity, reducing water and H+ permeability, promoting vesicle aggregation, and regulating ion conductances, all in a Ca2+-dependent manner. We have characterized a mouse in which a gene trap has been inserted into the first intron of annexin IV. Processing of the primary transcript is disrupted. Northern blot and immunoblot data indicated that annexin IV expression was eliminated in many but not all tissues. Immunohistochemical analysis, however, demonstrated that annexin IV expression was eliminated in some cell types, but was unaltered in others. 5'-Rapid amplification of cDNA ends analysis of intestinal and kidney RNA revealed three transcripts, AIVa, AIVb, and AIVc. AIVa is widely distributed. AIVb is expressed only in the digestive tract. AIVc expression is very restricted. A selected number of epithelial cells of unique morphology demonstrate high concentrations. All three transcripts produce an identical annexin IV protein. The different tissue and cell-specific expression profiles of the three transcripts suggest that regulation of both the annexin IV gene expression and the cellular role of the protein are complex. The AIVa-/- mouse may become a valuable model to further study transcription and the physiological role of annexin IV.

Structural and functional characterization of recombinant mouse annexin A11: influence of calcium binding

Annexin A11 is one of the 12 vertebrate subfamilies in the annexin superfamily of calcium/phospholipid-binding proteins, distinguishable by long, non-homologous N-termini rich in proline, glycine and tyrosine residues. As there is negligible structural information concerning this annexin subfamily apart from primary sequence data, we have cloned, expressed and purified recombinant mouse annexin A11 to investigate its structural and functional properties. CD spectroscopy reveals two main secondary-structure contributions, alpha-helix and random coil (approx. 30% each), corresponding mainly to the annexin C-terminal tetrad and the N-terminus respectively. On calcium binding, an increase in alpha-helix and a decrease in random coil are detected. Fluorescence spectroscopy reveals that its only tryptophan residue, located at the N-terminus, is completely exposed to the solvent; calcium binding promotes a change in tertiary structure, which does not affect this tryptophan residue but involves the movement of approximately four tyrosine residues to a more hydrophobic environment. These calcium-induced structural changes produce a significant thermal stabilization, with an increase of approx. 14 degrees C in the melting temperature. Annexin A11 binds to acidic phospholipids and to phosphatidylethanolamine in the presence of calcium; weaker calcium-independent binding to phosphatidylserine, phosphatidic acid and phosphatidylethanolamine was also observed. The calcium-dependent binding to phosphatidylserine is accompanied by an increase in alpha-helix and a decrease in random-coil contents, with translocation of the tryptophan residue towards a more hydrophobic environment. This protein induces vesicle aggregation but requires non-physiological calcium concentrations in vitro. A three-dimensional model, consistent with these data, was generated to conceptualize annexin A11 structure-function relationships.

Annexin II regulates multivesicular endosome biogenesis in the degradation pathway of animal cells

Proteins of the annexin family are believed to be involved in membrane-related processes, but their precise functions remain unclear. Here, we have made use of several experimental approaches, including pathological conditions, RNA interference and in vitro transport assays, to study the function of annexin II in the endocytic pathway. We find that annexin II is required for the biogenesis of multivesicular transport intermediates destined for late endosomes, by regulating budding from early endosomes-but not the membrane invagination process. Hence, the protein appears to be a necessary component of the machinery controlling endosomal membrane dynamics and multivesicular endosome biogenesis. We also find that annexin II interacts with cholesterol and that its subcellular distribution is modulated by the subcellular distribution of cholesterol, including in cells from patients with the cholesterol-storage disorder Niemann-Pick C. We conclude that annexin II forms cholesterol-containing platforms on early endosomal membranes, and that these platforms regulate the onset of the degradation pathway in animal cells.

Calcium-dependent conformational rearrangements and protein stability in chicken annexin A5

The conformational rearrangements that take place after calcium binding in chicken annexin A5 and a mutant lacking residues 3-10 were analyzed, in parallel with human annexin A5, by circular dichroism (CD), infrared spectroscopy (IR), and differential scanning calorimetry. Human and chicken annexins present a slightly different shape in the far-UV CD and IR spectra, but the main secondary-structure features are quite similar (70-80% alpha-helix). However, thermal stability of human annexin is significantly lower than its chicken counterpart (approximately 8 degrees C) and equivalent to the chicken N-terminally truncated form. The N-terminal extension contributes greatly to stabilize the overall annexin A5 structure. Infrared spectroscopy reveals the presence of two populations of alpha-helical structures, the canonical alpha-helices (approximately 1650 cm(-1)) and another, at a lower wavenumber (approximately 1634 cm(-1)), probably arising from helix-helix interactions or solvated alpha-helices. Saturation with calcium induces: alterations in the environment of the unique tryptophan residue of the recombinant proteins, as detected by near-UV CD spectroscopy; more compact tertiary structures that could account for the higher thermal stabilities (8 to 12 degrees C), this effect being higher for human annexin; and an increase in canonical alpha-helix percentage by a rearrangement of nonperiodical structure or 3(10) helices together with a variation in helix-helix interactions, as shown by amide I curve-fitting and 2D-IR.

Selective degradation of annexins by chaperone-mediated autophagy

Annexins are a family of proteins that bind phospholipids in a calcium-dependent manner. Analysis of the sequences of the different members of the annexin family revealed the presence of a pentapeptide biochemically related to KFERQ in some annexins but not in others. Such sequences have been proposed to be a targeting sequence for chaperone-mediated autophagy, a lysosomal pathway of protein degradation that is activated in confluent cells in response to removal of serum growth factors. We demonstrate that annexins II and VI, which contain KFERQ-like sequences, are degraded more rapidly in response to serum withdrawal, while annexins V and XI, without such sequences, are degraded at the same rate in the presence and absence of serum. Using isolated lysosomes, only the annexins containing KFERQ-like sequences are degraded by chaperone mediated-autophagy. Annexins V and XI could associate with lysosomes but did not enter the lysosomes and were not proteolytic substrates. Furthermore, four annexins containing KFERQ-like sequences, annexins I, II, IV, and VI, are enriched in lysosomes with high chaperone-mediated autophagy activity as expected for substrate proteins. These results provide striking evidence for the importance of KFERQ motifs in substrates of chaperone-mediated autophagy.