You really need to approach such situations with caution. Examination of the relatively small number of axial reflections probably show that there might be twofold screw axes in all three directions. But a non-crystallographic microscopic translation of nearly 0.5 in the direction of a crystallographic axis will give the same pattern of strong and weak reflections as a crystallographic twofold screw axis. If I were you, I would be very sure to try molecular replacement in all possible orthorhombic space groups. Several programs, including Phaser, will organize that exhaustive search across all eight possibilities for you.
On Mar 17, 2017, at 11:56 PM, Polisetty Satya Dev <[email protected]<mailto:[email protected]>> wrote: Hi, We checked all possible space groups of orthorhombic crystal system using Scala and Pointless but the statistics show that P212121 is the possible space group. Thank You, Satya Dev On Fri, Mar 17, 2017 at 8:03 PM, Teplyakov, Alexey [JRDUS] <[email protected]<mailto:[email protected]>> wrote: Check the space group. It may be orthorhombic with a pure rotational axis (e.g. P21212) or even monoclinic. From: CCP4 bulletin board [mailto:[email protected]<mailto:[email protected]>] On Behalf Of Polisetty Satya Dev Sent: Friday, March 17, 2017 9:51 AM To: [email protected]<mailto:[email protected]> Subject: [EXTERNAL] [ccp4bb] No improvement in R-factor after Refmac. Dear all, I solved a structure at 2.0 A resolution with R-work and R-free values 0.25 and 0.32 respectively and I am stuck at Refmac step where there is no further reduction in R-factor. The above stated values were obtained after several rounds of manual refinement followed by refmac. There are also areas where electron density is missing around peptide backbone in one of the monomer in ASU. Can anyone please tell me how can I improve the electron density and R-factor. The structure solution was obtained using Phaser MR and here are the data statistics: Average unit cell: 81.95, 100.40, 156.96, 90.00, 90.00, 90.00, Space group: P212121, Completeness 99.5, Multiplicity 6.4, Four monomers per ASU. Solvent content: 47%. Thank you everyone, Satya Dev, JNCASR.
