Confidence in Model-free output -- January 06, 2016 - 10:15

Hi Edward,

I am a last-year grad student working at a Max Planck Institute in Potsdam, 
Germany. My thesis is concerned with a Ca2+ binding protein. I collected full 
set of backbone relaxation data of the apo and holo form at two fields (600 
and 750) and saw a slight difference in R2 (about 10% decreased in holo 
form), some difference in R1 (slightly increased in holo form), and no change 
in NOE. However, after I run model free analysis (using the holo structure 
for both apo and holo form since no apo structure is available, all 9 
local_tm models, and all diffusion models), I saw a global tm difference of 
more than twofold and tremendous changes in s2 values in both forms with up 
to 50% decrease for the holo form. Is this a likely outcome? I do not know if 
I should trust model selection especially since the oblate model that was 
chosen needed about 200 iterations to converge. I used the Newton minimizing 
method. Below, I copied the AIC output from the console and the corresponding 
global tm values.

I'd be happy for any advice!

Thanks in advance,

Jonas


AIC model selection for apo form

Global model - all diffusion tensor parameters and spin specific model-free 
parameters.
# Data pipe                                  Num_params_(k)    
Num_data_sets_(n)    Chi2         Criterion
sphere - mf (Wed Dec 30 14:23:37 2015)       197               468            
      526.81736    920.81736
prolate - mf (Wed Dec 30 14:23:37 2015)      185               468            
      538.26716    908.26716
oblate - mf (Wed Dec 30 14:23:37 2015)       197               468            
      512.99733    906.99733
ellipsoid - mf (Wed Dec 30 14:23:37 2015)    197               468            
      518.69107    912.69107
The model from the data pipe 'oblate - mf (Wed Dec 30 14:23:37 2015)' has 
been selected.

Global tm = 1.5247e-08 s



AIC model selection for holo form

Global model - all diffusion tensor parameters and spin specific model-free 
parameters.
# Data pipe                                Num_params_(k)    
Num_data_sets_(n)    Chi2          Criterion
sphere - mf (Tue Jan  5 18:26:27 2016)     206               504              
    2305.05273    2717.05273
prolate - mf (Tue Jan  5 18:26:27 2016)    209               504              
    2299.94808    2717.94808
oblate - mf (Tue Jan  5 18:26:27 2016)     209               504              
    2281.81543    2699.81543
The model from the data pipe 'oblate - mf (Tue Jan  5 18:26:27 2016)' has 
been selected.

Global tm = 6.8584e-09 s