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I have had a solution of recombinant A that includes a very low
concentration of the contaminant B (so low that I missed it on the gel!)
This solution produces crystals of B (the wrong protein, of course)
that diffract to <1.5 Ang resolution (MALDI and N-terminal analysis of
about 60 of these tiny crystals led to a big disappointment!) I have
since been able to prepare pure A, but not pure B. The ratio of A:B
doesn't seem to affect the crystallizability of B, but I have considered
whether A acts as a precipitant and whether, say, BSA could act in the
same fashion.
kmj
Patrick Loll wrote:
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When attempting to crystallize the 1:1 complex of proteins A & B, we
get crystals that appear to contain A only, even though the
dissociation constant for A:B is quite low. This is not surprising
(albeit a tad annoying); the crystals grow at low pH and high salt, so
it's easy to understand how the complex might be disrupted.
However, B must be present, which I do find suprising; we only get
crystals when the mole ratio of A/B falls in the range 0.8-1.2.
I've heard of cases like this in the crystallization of protein:nucleic
acid complexes, but I'm not sure I've encountered one for a
protein:protein complex. Do others have similar anecdotes?
Thx,
Pat
------------------------------------------------------------------------
---------------
Patrick J. Loll, Ph. D. (215) 762-7706
Associate Professor FAX: (215) 762-4452
Department of Biochemistry & Molecular Biology
Director, Biochemistry Graduate Program
Drexel University College of Medicine
Room 10-102 New College Building
245 N. 15th St., Mailstop 497
Philadelphia, PA 19102-1192 USA
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