Dear all,

I need help interpreting results from a SRF; I am very naïve at interpreting them and would appreciate any pointer...

I have 2 crystals, before and after additive during crystallogenesis. They have different cell parameters, and I am wondering if I have a monomer or a dimer in the ASU, and if the additive changed this.

crystal w/o additive:
P21  114,5  107,6  134,6 beta=95,74   
1monomer in the ASU = 80% solvent, 1 dimer in the ASU = 61% solvent. Note that this high solvent content agrees well with the fact that this is a membrane protein, and diffracts both to low resolution and very anisotropic...    
SRF from Molrep:

+------------------------------------------+

 |       theta     phi     chi     P(i)/P(0)|
 +------------------------------------------+
 |   1     0.00    0.00    0.00        1.00 |
 |   2   148.48    0.00  180.00        0.51 |
 |   3   161.29    0.00  180.00        0.31 |
 |   4   105.34  180.00  180.00        0.30 |
 |   5    74.78  -56.26  179.58        0.27 |
 |   6    15.14 -163.78  180.00        0.25 |
 |   7    67.61  -40.16  180.00        0.24 |
 |   8   134.54 -180.00  180.00        0.19 |
 |   9    72.33  -37.82  180.00        0.18 |
 |  10    69.72   38.92  175.62        0.18 |
 |  11   110.28 -141.08  175.62        0.18 |
 |  12    96.58  101.90  179.79        0.18 |
 |  13    67.04  -15.02  179.71        0.18 |
 |  14    62.76  -15.52  179.45        0.17 |
 |  15   117.26  164.48  179.45        0.17 |
 |  16    68.39  -18.92  179.86        0.17 |
 |  17    70.52  -16.51  180.00        0.17 |
 |  18    24.05 -162.02  179.98        0.17 |
 |  19    78.61  -36.36  180.00        0.17 |
 |  20    83.17   78.42  173.34        0.16 |
 |  21    96.83 -101.58  173.34        0.16 |
 |  22    81.25  -75.03  179.73        0.16 |
 |  23    81.81  -17.73  180.00        0.16 |
 |  24    11.02 -142.22  180.00        0.16 |
 |  25    76.14  -16.64  179.71        0.16 |
 |  26    76.56  -16.93  180.00        0.16 |
 |  27   162.29   32.44  180.00        0.16 |
 |  28    10.03 -136.82  180.00        0.15 |
 |  29    68.67  -58.10  179.49        0.15 |
 |  30   111.33  121.90  179.49        0.15 |
 |  31    62.99  -20.19  180.00        0.14 |
 |  32    97.24  145.00  179.78        0.14 |
 |  33    99.56  165.86  179.74        0.14 |
 |  34    84.27  -82.68  180.00        0.14 |
 |  35    84.51   72.76  174.42        0.13 |
 +------------------------------------------+


Crystal with additive:
P21

CELL 117.2840 110.3330 155.6880 90.0000 93.4280 90.0000

1 monomer in the ASU = 84% solvent, 1 dimer = 68% solvent.

SRF from Molrep: 

 +------------------------------------------+
 |       theta     phi     chi     P(i)/P(0)|
 +------------------------------------------+
 |   1     0.00    0.00    0.00        1.00 |
 |   2    59.55    0.00  180.00        0.36 |
 |   3   156.11    0.00  180.00        0.29 |
 |   4    10.00 -165.58  180.00        0.26 |
 |   5   110.22 -180.00  180.00        0.26 |
 |   6    12.97 -169.15  180.00        0.23 |
 |   7   166.21   -9.06  180.00        0.22 |
 |   8    81.64   -9.61  179.74        0.21 |
 |   9    86.02   80.72  178.22        0.20 |
 |  10    93.98  -99.28  178.22        0.20 |
 |  11     5.96  -54.00  180.00        0.19 |
 |  12    67.40  -10.81  180.00        0.19 |
 |  13    87.10  -94.56  179.91        0.19 |
 |  14   147.13   47.70   10.71        0.19 |
 |  15   147.13  -47.70   10.71        0.19 |
 |  16    87.45   91.04  155.74        0.19 |
 |  17    92.55  -88.96  155.74        0.19 |
 |  18     5.33  -63.00  180.00        0.19 |
 |  19   104.60  169.61  179.59        0.19 |
 |  20    88.01  -85.32  179.05        0.18 |
 |  21    92.02   94.64  179.68        0.18 |
 |  22    87.61   91.31  153.16        0.18 |
 |  23    92.39  -88.69  153.16        0.18 |
 |  24     6.65  -46.80  180.00        0.18 |
 |  25   153.26   36.01   21.16        0.18 |
 |  26   153.26  -36.01   21.16        0.18 |
 |  27    63.11  -11.30  179.51        0.18 |
 |  28    76.82   -5.09  179.61        0.18 |
 |  29    87.69   91.37  148.72        0.18 |
 |  30    92.31  -88.63  148.72        0.18 |
 |  31    86.74   -9.44  179.90        0.17 |
 |  32    85.83   80.82  148.49        0.17 |
 |  33    94.17  -99.18  148.49        0.17 |
 |  34   175.25   57.61  180.00        0.17 |
 |  35     4.63  -90.00  180.00        0.17 |
 +------------------------------------------+

Can I say that the peak at 0.51 in the crystal without additive is significant, concluding that there is probably a dimer in the ASU in that crystal, in contrast to the crystal with additive where no peak stands out, which would lean towards a monomer in the ASU?

Thank you for your help.
Best
Vincent



--

Vincent Chaptal, PhD

Institut de Biologie et Chimie des Protéines

Drug Resistance and Membrane Proteins Laboratory

7 passage du Vercors 

69007 LYON

FRANCE

+33 4 37 65 29 01

http://www.ibcp.fr