Overlapping and specific patterns of GDNF,c-ret and GFR alpha mRNA expression in the developing chicken retina

GDNF and the GDNF receptors, c-Ret, GFR alpha 1 and 2 mRNA is expressed in the developing chicken retina. GDNF labelling was mainly found in embryonic day 4-5 retina but weak labelling could also be found over scattered retinal cells at later stages. c-ret labelling was found over ganglion cells, amacrine and horizontal cells; the preferred GDNF receptor (GFR alpha 1) over amacrine and horizontal cells; and the less preferred GDNF receptor (GFR alpha 2) over ganglion cells, amacrine cells and photoreceptors.     

Enantiomeric separations of amino alcohols by packed-column SFC on Hypercarb with L-(+)-tartaric acid as chiral selector

The use of L-(+)-tartaric acid as a chiral mobile phase additive (CMPA) has been investigated in a packed-column SFC system. The CMPA, carbon dioxide, and methanol, containing a high concentration of aliphatic amine additive, were used as the mobile phase and Hypercarb as support [Gyllenhaal O., Karlsson A., SFC of metoprolol and other amino alcohols on Hypercarb (in preparation)]. Good enantioselectivities were obtained for tertiary amine homologues of 2-amino alcohols, used as beta-adrenoreceptor-blocking drugs. Moderate selectivities were observed for aromatic compounds having a second substituent in the ortho-position. The overall retention was influenced by the aromaticity of the analytes as well as the presence of free electron pairs in the molecule. Increased concentrations of CMPA gave higher retention and also increased the enantioselectivity. The practical utility of this present enantioselective system was demonstrated on one batch of (S)-metoprolol that was N-methylated with methyl iodide. The enantiomeric separation was accomplished within 10 min.     

Interaction of Axl receptor tyrosine kinase with C1-TEN,a novel C1 domain-containing protein with homology to tensin

Axl receptor tyrosine kinase is implicated in several malignancies and is the receptor for the vitamin K-dependent growth factor Gas6. From a yeast two-hybrid screen of protein-protein interactions with the Axl cytoplasmic domain, we detected a previously uncharacterised SH2 domain-containing protein. We cloned two novel splice variants of this protein that give rise to 1409- and 1419-amino acid proteins, differing only in their N-terminal residues and yielding a 150-kDa protein product by in vitro translation. The Axl-interacting C-terminus contains a tandem SH2 and PTB domain combination homologous to the focal adhesion protein tensin. We detected interaction of Axl with both domains in mammalian cells by co-immunoprecipitation and two-hybrid analyses. In addition, the protein possesses an N-terminal putative phorbol ester-binding C1 domain as well as a central tyrosine phosphatase motif. Thus, we have named the protein C1 domain-containing phosphatase and TENsin homologue (C1-TEN). Northern blot analysis of C1-TEN in human tissues revealed highest expression in heart, kidney, and liver. In summary, we have identified a novel multi-domain intracellular protein that interacts with Axl and which may furthermore be involved in other signal transduction pathways.     

Dramatic stabilization of the native state of human carbonic anhydrase II by an engineered disulfide bond

To find a disulfide pair that could stabilize the enzyme human carbonic anhydrase II (HCA II), we grafted the disulfide bridge from the related and unusually stable carbonic anhydrase form from Neisseria gonorrhoeae (NGCA) into the human enzyme. Thus, the two Cys residues at positions 23 and 203 were engineered into a pseudo-wild-type form of HCA II (C206S), giving the mutant C206S/A23C/L203C. The disulfide bond was not formed spontaneously. The native state of the reduced form of the mutant was markedly destabilized (2.9 kcal/mol) compared to that of HCA II. Formation of a disulfide bridge was achieved by treatment by oxidized glutathione. This led to a significant stabilization of the native conformation. Compared to HCA II the unfolding midpoint for the variant was increased from 0.9 to 1.7 M guanidine HCl, corresponding to a stabilization of 3.7 kcal/mol. This makes the human enzyme almost as stable as the model protein NGCA, for which the unfolding of the native state has a midpoint at 2.1 M guanidine HCl. The stabilized protein underwent, contrary to all other investigated variants of HCA II, an apparent two-state unfolding transition, as judged from intrinsic Trp fluorescence measurements. A molten-globule intermediate is nevertheless formed but is suppressed because of the high denaturant pressure it faces upon rupture of the native state.     

The solution structure of the CBM4-2 carbohydrate binding module from a thermostable Rhodothermus marinus xylanase

The solution structure is presented for the second family 4 carbohydrate binding module (CBM4-2) of xylanase 10A from the thermophilic bacterium Rhodothermus marinus. CBM4-2, which binds xylan tightly, has a beta-sandwich structure formed by 11 strands, and contains a prominent cleft. From NMR titrations, it is shown that the cleft is the binding site for xylan, and that the main amino acids interacting with xylan are Asn31, Tyr69, Glu72, Phe110, Arg115, and His146. Key liganding residues are Tyr69 and Phe110, which form stacking interactions with the sugar. It is suggested that the loops on which the rings are displayed can alter their conformation on substrate binding, which may have functional importance. Comparison both with other family 4 cellulose binding modules and with the structurally similar family 22 xylan binding module shows that the key aromatic residues are in similar positions, and that the bottom of the cleft is much more hydrophobic in the cellulose binding modules than the xylan binding proteins. It is concluded that substrate specificity is determined by a combination of ring orientation and the nature of the residues lining the bottom of the binding cleft.     

The N terminus of the MUC2 mucin forms trimers that are held together within a trypsin-resistant core fragment

The N terminus of the human MUC2 mucin (amino acids 1-1397) has been expressed as a recombinant tagged protein in Chinese hamster ovary cells. The intracellular form was found to be an endoglycosidase H-sensitive monomer, whereas the secreted form was an oligomer that gave monomers upon disulfide bond reduction. The secreted MUC2 N terminus contained a trypsin-resistant core fragment. Edman sequencing and mass spectrometry of the peptides obtained localized this core fragment to the C-terminal end of the recombinant protein. This core retained its oligomeric nature with an apparent mass of approximately 240 kDa. Upon reduction, peptides of approximately 85 kDa were found, suggesting that the N terminus forms trimers. This interpretation was also supported by gel electrophoresis and gel filtration of the intact MUC2 N terminus. Electron microscopy revealed three globular domains each linked via an extended and flexible region to a central part in a trefoil-like manner. Immunostaining with gold-labeled antibodies localized the N-terminal end to the three globular structures, and the antibodies directed against the Myc and green fluorescent protein tags attached at the C terminus localized these to the stalk side of the central trefoil. The N terminus of the MUC2 mucin is thus assembled into trimers that contain proteolytically stable parts, suggesting that MUC2 can only be partly degraded by intestinal proteases and thus is able to maintain a mucin network protecting the intestine.     

Fragmentation of dihydroxyacetone kinase 1 from Saccharomyces cerevisiae indicates a two-domain structure

Global protein expression in Saccharomyces cerevisiae strains either deleted for both yeast dihydroxyacetone kinases (DAK1 and DAK2) or overexpressing DAK1, was characterized by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). We found protein expression in the double deletion strain to be highly similar to wild-type. In the strain overexpressing Dak1p, nine spots representing fragments of the Dak1p protein in the size range 40-20 kDa and amounting to approximately 30% of total Dak1p, were discovered (native size Dak1p migrates at roughly 60 kDa). Fragments were characterized by matrix-assisted laser desorption/ionization mass spectrometry and electrospray mass spectrometry analyses to represent either the N- or the C-terminal part of the DAK1 protein. Cleavage points, predicted from mass spectrometry and 2-D PAGE data, mapped almost exclusively in the middle region showing low sequence conservation between Dak1p and its closest homologues. We hypothesize that observed Dak1p fragments represent stable structural domains shielded from access by native endoproteases. Furthermore, overexpressing Dak1p with the non-native N-terminus (M)A-, resulted in native size Dak1p and N-terminal Dak1p fragments appearing in two major 2-D PAGE forms of approximately equal size and abundance, but with slightly different isoelectric points. However, when overexpressing Dak1p with the native N-terminus (M)S-, only the more acidic 2-D PAGE form appeared. In the N-terminal acetyltransferase mutant nat1delta, (M)A-Dak1p species were converted into the basic form, arguing twin spots to represent forms with acetylated and deacetylated N-termini. Data thus indicated that (M)A-N-termini, in the Dak1p context, were NatA substrates recognized with 50% lower efficiency than (M)S-N-termini.     

Analysis of human alpha-thrombin by hydrophobic interaction high-performance liquid chromatography

The major active form of human thrombin, alpha-thrombin, was analyzed by hydrophobic interaction high-performance liquid chromatography (HIC-HPLC). The chromatographic system included a polymeric phenyl column and elution was performed by a gradient, 2-0M sodium chloride (5-20 min). Total analysis time was 30 min per injection. By this method, a good resolution between alpha-thrombin and the proteolytically modified thrombin forms, beta- and gamma-thrombin, was obtained. In addition, the thrombin preforms, prothrombin, prethrombin 1, and prethrombin 2, were also resolved from alpha-thrombin in the system. The results from the HIC method were compared to those obtained from non-reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By this high-resolution chromatographic method, the rapid analysis of purified alpha-thrombin is possible.