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Histidyl Residues (histidyl + residue)
Selected AbstractsTransitions of serum albumin in patients with glomerulosclerosis ,in vivo' characterization by electrophoretic titration curvesELECTROPHORESIS, Issue 14 2006Maurizio Bruschi Abstract HSA functions as a physiological transporter of solutes and small molecules that induce structural transitions ,in vitro'. Analysis of these transitions requires prior purification of HSA that could introduce bias due to conformational changes. We utilized electrophoretic titration curves to describe a neutral to acid (N,A) transition of HSA directly in sera of seven patients with active focal segmental glomerulosclerosis (FSGS). The divergent electrophoretic profile of HSA was characterized by a shift in the range of pHs between 4.5 and 7.5 with an average variation of free electrophoretic mobility corresponding to loss of 1 positive charge in the pKa protonation range of histidyl residues and should involve domain I of HSA. ,In-gel' determination by maleimide-PEO2-biotin of free SH 34 of domain I showed inaccessibility of the dye at this site in pathological HSA and alkylation with the same complex induced N,A transition in normal HSA. Potential binders of free imidazoles such as Ca++ and/or of SH 34 such as NO were excluded on the basis of direct titration and studies on binding stimulation. This is the first report describing a transition of HSA directly ,in vivo', and the utilization of electrophoretic titration curves was critical to this purpose. This transition appears to be specific to FSGS and is unrelated to the nephrotic syndrome, Ca++ and NO binding. Spectroscopic analysis will elucidate the structural implication. [source] Zinc improves gene transfer mediated by DNA/cationic polymer complexesTHE JOURNAL OF GENE MEDICINE, Issue 5 2002Chantal Pichon Abstract Background The weak efficiency of plasmid transfer into the cytosol remains one of the major limiting factors to achieve an efficient transfection with DNA/cationic polymer complexes. We found that divalent metal Zn2+ can improve the polyfection efficiency, especially with DNA/histidylated polylysine (His-pLK) complexes. Methods and results The supplementation of the transfection medium with 250 µM ZnCl2 increased the polyfection of human hepatocarcinoma (HepG2) cells with a plasmid encoding EGFP complexed with pLK, polyethyleneimine and His-pLK. Zn2+ is more efficient on DNA/His-pLK complexes: the number of EGFP-positive cells increased from 1% to more than 40%. This phenomenon is selective to Zn2+ because no effect was obtained with other divalent cations. The effect of zinc varies from cell to cell. The binding of Zn2+ to histidyl residues might increase zinc endosomal concentration favoring membrane fusion. Flow cytometry and confocal microscopy studies clearly indicate that with His-pLK, the plasmid is better delivered in the cytosol as well as in the cell nucleus in zinc-treated cells. An investigation conducted with the histidine-rich peptide H5WYG showed that zinc inhibits membrane permeabilization but promotes membrane fusion as evidenced by resonance energy transfer. Conclusions Data reported here imply that the addition of zinc ions in the transfection medium can trigger an increase of the fusion of endosomes containing polyplexes which is more effective in the presence of histidine-rich molecules. Consequently, the amount of plasmid in the cytosol available to reach the nucleus is increased leading to an improvement of polyfection. Copyright © 2002 John Wiley & Sons, Ltd. [source] Observation of a calcium-binding site in the ,-class carbonic anhydrase from Pyrococcus horikoshiiACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2008Jeyaraman Jeyakanthan Carbonic anhydrases are zinc-containing metalloenzymes that catalyze the interconversion of carbon dioxide and bicarbonate. Three crystal structures of ,-class carbonic anhydrase (one of which is bound to a bicarbonate molecule) from the aerobic OT3 strain of the hyperthermophilic archeon Pyrococcus horikoshii have been solved by molecular replacement in space group F4132. The asymmetric unit contains a monomer of 173 amino acids and a catalytic Zn2+ ion. The protein fold is a regular prism formed by a left-handed ,-helix, similar to previously reported structures. The active-site Zn2+ ion located at the interface between the two monomers is bound to three histidyl residues and a water molecule in a tetrahedral fashion. In addition to the 20 ,-strands comprising the ,-helix, there is also a long C-terminal ,-helix. For the first time, Ca2+ ions have been observed in addition to the catalytic Zn2+ ion. It is hypothesized that Tyr159 (which corresponds to the catalytically important Asn202 in previously reported structures) utilizes C,H..., interactions to fulfill its functions. This study may shed light on the catalytic mechanism of the enzyme and throw open new questions on the mechanism of product removal in carbonic anhydrases. [source] Liganded and unliganded forms of Antarctic fish haemoglobins in polyethylene glycol: crystallization of an R-state haemichrome intermediateACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2001Antonio Riccio Liganded and unliganded forms of two Antarctic fish haemoglobins, from Trematomus newnesi and T. bernacchii, have been crystallized in low-salt media using polyethylene glycol as precipitant. In particular, crystals of air-exposed T. newnesi carbomonoxy haemoglobin were found to be isomorphous to the crystals grown in high-salt media. Preliminary X-ray analysis of the diffraction data revealed that the ,-haem iron of this haemoglobin is in the haemichrome state, with both the proximal and distal histidyl residues linked to the iron. This is the first crystallization of a haemichrome intermediate of a vertebrate haemoglobin. [source] | ||||||||||