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AIM: Total mesorectal excision (TME) has been shown to improve the outcome for patients with rectal cancer. In contrast, there are fewer data on complete mesocolic excision (CME) for colonic cancer.METHOD: Data from the National Colorectal Cancer Database were analysed. This includes about 95% of all patients with colorectal cancer in Denmark. Only patients having elective surgery for colonic cancer in the period 2001-2008 were included. Overall and relative survival analyses were carried out. The study period was divided into the periods 2001-2004 and 2005-2008.RESULTS: 9149 patients were included for the final analysis. The overall 5-year survival rates were 0.65 in 2001-2004 and 0.66 in 2005-2008. The relative 5-year survival rates were also within 1% of each other. None of these comparisons was statistically significant.CONCLUSION: Survival following elective colon cancer surgery has been almost unchanged since 2001.

Udgivelsesdato: August 8th

Molecular dynamics simulations of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers using the CHARMM27 force field in the tensionless isothermal-isobaric (NPT) ensemble give highly ordered, gel-like bilayers with an area per lipid of ∼48 Å2. To obtain fluid (Lα) phase properties of DPPC bilayers represented by the CHARMM energy function in this ensemble, we reparameterized the atomic partial charges in the lipid headgroup and upper parts of the acyl chains. The new charges were determined from the electron structure using both the Mulliken method and the restricted electrostatic potential fitting method. We tested the derived charges in molecular dynamics simulations of a fully hydrated DPPC bilayer. Only the simulation with the new restricted electrostatic potential charges shows significant improvements compared with simulations using the original CHARMM27 force field resulting in an area per lipid of 60.4 ± 0.1 Å2. Compared to the 48 Å2, the new value of 60.4 Å2 is in fair agreement with the experimental value of 64 Å2. In addition, the simulated order parameter profile and electron density profile are in satisfactory agreement with experimental data. Thus, the biologically more interesting fluid phase of DPPC bilayers can now be simulated in all-atom simulations in the NPT ensemble by employing our modified CHARMM27 force field.

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Metallo-beta-lactamases are bacterial enzymes that may function with either one or two zinc ions bound in the active site. In this work, the binding of benzylpenicillin to mono-zinc metallo-beta-lactamase from Bacillus cereus has been investigated in a docking procedure applying a combined quantum mechanical/molecular mechanical method as the final step. It is demonstrated that the substrate can bind with the carbonyl oxygen of the lactam ring coordinating to the zinc ion, and with the zinc-bound hydroxide ion in position for a nucleophilic attack on the carbonyl carbon of the lactam ring. In some structures, both the histidine and the cysteine at the other (unoccupied) metal-binding site are in a proper position to function as proton shuttles in proton transfer from the previously zinc-bound hydroxide, to the nitrogen in the lactam ring. In addition, the hydrophobic region formed by Phe34, Val39, Trp59, and Ala89 interacts with the phenyl group of benzylpenicillin, whereas the carboxylate group may be stabilized by Lys171 and Asn180. Alternatively, the carboxylate can bind to the zinc ion, prohibiting the nucleophilic attack of the zinc-bound hydroxide on the lactam carbonyl carbon. However, such a structure is energetically disfavored compared to the other enzyme-substrate complexes.

Two central steps in the hydrolysis of lactam antibiotics catalyzed by mononuclear metallo-beta-lactamases, formation of the tetrahedral intermediate and its breakdown by proton transfer, are studied for model systems using the density functional B3LYP method. Metallo-beta-lactamases have two metal ion binding sites, one of which is occupied in the mononuclear species. In this work it is assumed that catalysis takes place at zinc site 1, which is modeled by the metal ion, three imidazole rings, and a hydroxide ion. The lactam ring, a minimal model of beta-lactam antibiotics, is initially coordinating to the zinc ion. Potential proton shuttles from the second (unoccupied) metal-binding site (water, Asp, or Cys) are included in some calculations. The calculated reaction barrier for formation of the tetrahedral intermediate is 13 kcal/mol, close to what is observed experimentally for the rate-limiting step. The barrier for the breakdown of the intermediate is low, 0-10 kcal/mol, if it is assisted by a water molecule or by a Cys or Asp model. Thus, the results indicate that proton transfer is not rate-limiting, and that any of the residues from the second metal site may function as proton shuttle. For most studied systems, the tetrahedral structure is a stable intermediate. Moreover, the C-N bond in the lactam ring is intact in this intermediate, as well as in the following transition state-its cleavage is induced by proton transfer to the nitrogen atom in the lactam ring. However, for the model with Asp as a proton shuttle, attack of the zinc-bond hydroxide ion seems to be concerted with the proton transfer. We have also studied the effect of replacing one of the histidine ligands by an asparagine or glutamine residue, giving a zinc site representative of other subclasses of metallo-beta-lactamases. This has only a small effect on the calculated reaction barriers. Likewise, if the zinc ion is replaced by cadmium, only small changes in the reaction barrier for proton tr

Models of the metal ion binding sites of native ZnZn and of cadmium-substituted ZnCd and CdCd phosphotriesterase, including full amino acid side chains, were geometry optimized with quantum mechanical methods, with effective fragment potentials (EFP) representing the protein environment surrounding the active site. One to three water molecules were included in the active site in addition to the bridging hydroxide. Comparison with recent X-ray diffraction results Benning, M. M.; Shim, H.; Raushel, F. M.; Holden, H. M. Biochemistry 2001, 40, 2712-22 is hindered by the presence of ethylene glycol molecules in the active site. We suggest that the ethylene glycol required for crystallization distorts the structure of the water network in the active site and that the theoretical structures provide a better description of the system in aqueous solution. Cd-113 NMR isotropic shielding calculations were performed to analyze the experimentally determined chemical shifts at 212 and 116 ppm, respectively, for the CdCd enzyme. The calculated isotropic shieldings correlate with the coordination number of the metal ions, indicating that the CdCd enzyme has one more ligand at the high shift site than at the low shift site. Theoretically, a number of energetically close structures are found for the CdCd structure. Formally, one of these agrees with the X-ray structure and is supported by the NMR assignment. For the hybrid ZnCd enzyme, the most stable theoretical structure is Cd1Zn2, with the metal bound to the Od1 of the carboxylate of the first-shell aspartate designated M 1, but the energy difference between Cd1Zn2 and the lowest energy Zn1Cd2 structure is only about 2 kcal/mol and decreasing with the addition of water molecules. The Zn1Cd2 arrangement is found experimentally.