[phenixbb] Challenging Mol.Rep. Problem

Mo Wong mowong22 at gmail.com
Tue Dec 9 10:31:11 PST 2014

Hi all,

I’m stuck on a rather complex molecular replacement problem. The crystals
are of an antigen-Fab complex totaling ~67 kDa (waiting to confirm using
PAGE gel). They diffract to ~3.5A at the synchrotron and process in C2 with
dimensions 220x130x230 and beta at 103 so it looks like there are round
9to12-ish copies in the ASU. The overall Rmerge is high at ~25% with I/sig
cutoff ~2 and redundancy of 5; however, at 4.5A this drops to ~15%.
Furthermore, processing in P1 gives similar Rmerge values too.

Self-Patterson doesn’t suggest translational symmetry, but the
self-rotation function (SRF) suggests high NCS (see below/attached).

I’m hoping the SRF might be helpful in trying to confirm/dismiss C2 is the
likely space group, and perhaps suggest a logical assembly with the ASU (I
see strong 2-fold and 3-fold NCS operators suggesting to me dimeric trimers
or vice versa - however, I’ve never had to really analyze SRFs in the
absence of a mol. rep. solution so my interpretation could be wrong).

Anyway, any help to bringing a molecular replacement solution closer to
reality would be appreciated.


[image: Inline image 1]
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