aniso scaling

["Heroux, Annie" <heroux@sri.org>]

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Dear All,

I am refining a structure at 2.3 A resolution. I have a tetramer in the
asymmetric unit. I am using STRICT NCS and group B's (2 per residue: main
chain atoms and side chains atoms).
I always start a refinement using XPLOR and I finish it with REFMAC because
I find it easier to manipulate alternate conformations (that won't happen in
this case!!) but also because the anisotropic scaling seems to work better.
Is it?

The scaling in XPLOR gives:

SCALEF: k=    0.170  B11=  -1.221 B22=  18.857 B33=   7.993 B12=   0.000
B13= -10.499 B23=   0.000

It sure looks like it needs some aniso scaling.

That makes my R and Rfree drop almost 4% each after bulksolvent correction,
powell minimization and some B refinement.  However, in XPLOR I noticed that
after the anisotropic scaling my B's go up and up and up (before average B
is 28 and after scaling, it's 40!!!!! And it continues to go up after each
cycle). The problem is I don't know what is going on with those B and I
don't have any confidence in them. They also don't make any sense. Some of
the main chain atoms will have B's higher than the side chain atoms in the
same residue. 
This happens not only for this structure but for all of the one I work on.
It is also obvious when you retrieve some of the pdb files in the Data Bank.
Am I the only one worried about it?

Can someone shed some light on that matter please?

Here are statistics from Moleman for before and after some refinement.

Before:

powell16c		R = 0.306181  FREE-R = 0.320428		15-2.3 A
with 2.0 sigma cutoff
	====================================================================
	 Chain name      Atoms       Bave       Bsdv       Bmin       Bmax
	    <->A1          942      28.61      10.36      13.20      73.83
	    <->A2          804      32.89      10.33      14.71      65.89
	    <->AL           23      32.05       2.54      27.81      38.12
	    <->AM            1      35.18    1237.63      35.18      35.18
	    <->AW           15      34.38       0.00      34.38      34.38
	====================================================================

After: 

powell17c	R = 0.26149  FREE-R = 0.283608		aniso scaling 15-2.3
A with 2.0 sigma cutoff 
	====================================================================
	 Chain name      Atoms       Bave       Bsdv       Bmin       Bmax
	    <->A1          942      40.91      11.09      18.80      85.51
	    <->A2          804      45.33      10.73      22.57      82.86
	    <->AL           23      39.15       5.76      30.00      50.88
	    <->AM            1      46.41    2153.89      46.41      46.41
	    <->AW           15      46.80       0.01      46.80      46.80
	 Nr of chains encountered  : (          5) 
	====================================================================


I used the XTALMACRO:scalef in XPLOR.

Thanks
Annie
+++++++++++++++++++++++++++
Annie Heroux
Southern Research Institute
2000 Ninth Avenue S.
Birmingham, AL 35205
(205) 581-2375
heroux@sri.org
+++++++++++++++++++++++++++