Computational protocol: The dynamic organization of fungal acetyl-CoA carboxylase

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[…] All X-ray diffraction data were collected at beamlines X06SA (PXI) or X06DA (PXIII) at the Swiss Light Source (SLS, Paul Scherrer Institute, Villigen, Switzerland) equipped with PILATUS detectors. The wavelength of data collection was 1.000 Å for native crystals, and 1.527 and 1.907 Å for crystals derivatized with europium and cadmium, respectively. Raw data were processed using XDS. Molecular replacement was carried out using Phaser 2.5.7 and 2.6.0, density modification was performed using Parrot and resolve, multicrystal averaging was carried out using phenix. All model building procedures were conducted using Coot and figures were prepared using PyMOL (Schrödinger LLC).Diffraction of initial SceCD crystals in space group P43212 with unit cell dimensions of a=b=110.3 Å and c=131.7 Å was limited to 3.5 Å. The resolution was improved to 3 Å by addition of trimethylamine or benzamidine to the reservoir solution without significant changes in unit cell dimensions. Crystals derivatized with thimerosal and europium were used for initial SAD phase determination using the SHELXC/D package. Two mercury and four europium sites were located, and an initial model was placed in the resulting maps. Since crystals derivatized with europium were slightly non-isomorphous with a c axis length of 127 Å, multicrystal averaging was used for density modification and provided directly interpretable maps. Iterative cycles of model building and refinement in Buster (version 2.10.2; Global Phasing Ltd) converged at Rwork/Rfree of 0.20/0.24. The final model lacks the disordered N terminus (amino acids 768–789), an extended loop in the CDC1 domain (1,203–1,215), a short stretch (1,147–1,149) preceding the regulatory loop and the two very C-terminal residues (1,493–1,494). On the basis of temperature factor analysis, the start and end of the regulatory loop show higher disorder than the region around the interacting phosphoserine 1157. MS analysis of dissolved crystals detected quantitative phosphorylation of the regulatory Ser1157, as also found for full-length SceACC, and additionally albeit with much lower occurrence, phosphorylation of Ser790, Ser1137, Ser1148 and Ser1159. A modelled phosphoryl position for Ser1159 could overlap with the one of Ser1157, and might be represented in the crystal. For all other phosphorylation sites no difference density could be observed, probably because of very low occupancy. PDBeFold was used to search for structural homologues. The thresholds for lowest acceptable percentage of matched secondary structure elements were 70% for the search query and 20% for the result.Initial HsaBT-CD crystals were obtained in space group I4122 with a=b=240.1 Å and c=768.9 Å and diffracted to 7.5 Å. Optimized and dehydrated crystals also belonged to space group I4122 but with unit cell parameters a=b=267.3 Å and c=210.6 Å and diffracted to a resolution of 3.7 Å. Phase information was obtained from SAD based on bound cadmium ions from the crystallization condition. Six cadmium positions were located in a 4.0-Å resolution data set at 1.9 Å wavelength using SHELXC/D via the HKL2MAP interface. Density modification and phasing based on this anomalous data set, a 3.7-Å resolution data set at 1.0 Å wavelength and additional non-isomorphous lower-resolution data sets led to a high-quality electron density map. At the intermediate resolution obtained, the map was interpreted by a poly-alanine model, which was guided by predicted secondary structure as well as sequence and structural alignment with SceCD. The final model contains five cadmium ions and refines using phenix against experimental data with Rwork/Rfree of 0.35/0.38, as expected for a poly-alanine model. Two HsaBT-CD monomers are packed in the asymmetric unit via the CDN and BT domains. Density on top of the β-barrel of one BT most likely representing parts of the BT–CD linker guided the assignment of this BT to its linked CD partner domain. This BT-to-CD assignment was further supported by the analysis of an additional lower-resolution crystal form. Cadmium ions were found to participate in crystal packing.In HsaACC, phosphorylation at regulatory sites was detected as provided in the main text. No phosphorylation was detected for other phosphosites previously identified in large-scale phosphoproteomics studies, namely serines 5, 23, 25, 48, 53, 78, 488, 786, 1273 (refs , , ).Two different crystal forms were obtained for CthCD-CTCter (denoted as CthCD-CTCter1 and CthCD-CTCter2), diffracting to 3.6 and 4.5 Å. Both forms packed in space group P212121 with unit cell constants of a=97.7 Å, b=165.3 Å and c=219.2 Å or a=100.2 Å, b=153.5 Å and c=249.2 Å, respectively. Phases were determined by molecular replacement using a homology model based on SceCT (pdb 1od2) as search model in Phaser; multicrystal averaging was applied in density modification. The CT domain was rebuilt and an initial homology model based on the SceCD structure was fitted into difference density for CthCD-CTCter1. Iterative cycles of rebuilding and refinement in Buster converged at Rwork/Rfree of 0.20/0.24. The refined CD fragment served as a starting model for rebuilding CthCD-CTCter2 at lower resolution. Coordinate refinement in Buster was additionally guided by reference model restraints and converged at Rwork/Rfree of 0.24/0.24. Residues 1,114–1,185, 1,213–1,252, 1,380–1,385, 1,465–1,468 and 2,188–2,195 were disordered in both crystal forms and are not included in the models. Helical regions C terminal to Glu2264 of both protomers of CthCD-CTCter1 and C terminal to Leu2259 and Arg2261 of the two protomers of CthCD-CTCter2, respectively, could not be built unambiguously and were therefore interpreted by placing poly-alanine stretches. Conservation was mapped on the CthCD-CTCter1 crystal structure using al2co based on a sequence alignment of 367 fungal ACC sequences calculated by Clustal Omega. MS analysis of purified protein detected 7% phosphorylation at Ser1170 (corresponding to Ser1157 in SceCD).CthCD-CT crystallized in space group P31212 with unit cell constants of a=b=195.0 Å and c=189.5 Å and crystals diffracted to a resolution of 7.2 Å. The structure was solved by molecular replacement using a model composed of CthCT and CDC2 as search model in Phaser. CDC1 and CDN were placed manually into the resulting maps, and the model was refined using rigid-body, domain-wise TLS and B-factor refinement and NCS- and reference model-restrained coordinate refinement in Buster to Rwork/Rfree of 0.23/0.25. Owing to the low resolution, the maximum allowed B-factor in Buster refinement was increased from the default value of 300–500 Å2, minimizing B-factor clipping to 5% of all atoms. Residues 1,033–1,035, 1,134–1,152, 1,213–1,252, 1,380–1,385, 1,465–1,468 and 2,188–2,195 were not included in the models. Helical regions C terminal to Leu2259 and Arg2261 on the two protomers, respectively, were interpreted as described for CthCD-CTCter. Loop conformations, including the regulatory loop, were modelled as observed in SceCD. MS analysis of purified protein detected 60% phosphorylation at Ser1170 (corresponding to Ser1157 in SceCD). Conservation was mapped on the CthCD-CT crystal structure as for CthCD-CTCter.CthΔBCCP ACC crystallized in space group P6422 with unit cell constants of a=b=462.2 Å and c=204.6 Å, resolution was limited to 8.4 Å. Structure determination and refinement was performed as for CthCD-CT, with a maximum allowed B-factor of 500 Å2, minimizing B-factor clipping to 3% of all atoms. Although substantial difference density is observed, no defined positions of the BT and BC domains could be derived because of disorder or partial in situ proteolysis or combinations thereof. In addition, residues 1,032–1,039, 1,134–1,152, 1,213–1,252, 1,380–1,385, 1,465–1,468 and 2,188–2,195 were not included in the model. The MissingAtom macro implemented in Buster was employed to account for missing atoms, the final Rwork/Rfree were 0.30/0.32. A region C terminal to Leu2259 on one protomer was interpreted as poly-alanine. Loop conformations, including the regulatory loop, were modelled as observed in SceCD. MS analysis of purified protein detected 70% phosphorylation at Ser1170 (corresponding to Ser1157 in SceCD). [...] Proteins were thawed on ice and dialysed overnight against 30 mM MOPS pH 7, 200 mM ammonium sulfate, 5% glycerol and 10 mM dithiothreitol. Raw scattering data were measured at SAXS beamline B21 at Diamond Light Source. The samples were measured at concentrations of 2.5, 5 and 10 mg ml−1. Data were processed using the ATSAS package according to standard procedures. A slight increase in scattering in the very low-resolution range was observed with increasing protein concentrations, which may be because of interparticle attraction or minor aggregation. Scattering intensities were thus extrapolated to zero concentration using point-wise extrapolation implemented in Primus. Direct comparison of raw scattering curves demonstrates the similarity of CthACC and CthΔBCCP, and the derived values such as Rg and Porod Volume match within expected error margins. Molecular mass estimations based on the SAXS–MOW method derive values of 534.7 and 534.0 kDa for CthACC and CthΔBCCP, respectively. The relative discrepancies to the theoretical weights of 516.8 kDa (CthACC) and 503.0 kDa (CthΔBCCP) are 3.5% and 6.2%, respectively, which is in a typical range for this method. […]

Pipeline specifications

Software tools XDS, PHENIX, Coot, PyMOL, SHELX, PDBeFold, HKL2MAP, AL2CO, Clustal Omega, ATSAS
Applications Small-angle scattering, Protein structure analysis
Organisms Saccharomyces cerevisiae
Diseases Metabolic Diseases, Neoplasms, Hereditary Central Nervous System Demyelinating Diseases
Chemicals Acetyl Coenzyme A, Adenosine Triphosphate, Malonyl Coenzyme A