AutoMR and capsids
Dear all, I am currently trying to use AutoMR to do molecular replacement on an icosahedral virus capsid. It is a T=1 capsid so there are 60 copies of the monomer per capsid and based on the Matthews coefficient there are ~3 capsids in the unit cell. The search model is 99% identical (thank God) but I am unsure how to approach this. Do I used the 60-mer as the model and search for three copies? Do I use a monomer for the model and search for 180 copies? Should I break the model down to smaller pieces (i.e. a 30-mer and copies=6, or 12-mer and copies=15)? I would appreciate any help I can get on this one. Thanks, Katherine -- SIPPEL,KATHERINE H Ph. D. candidate Department of Biochemistry and Molecular Biology College of Medicine University of Florida
Dear Katherine, If you're sure that there are 3 full copies (and that you couldn't, say, have six half-copies sitting on crystallographic 2-folds), the best would be to search for full capsids. Now, for each copy there are 60 different ways that the capsid could be oriented, but the version of Phaser distributed with the latest Phenix release should recognize the internal symmetry -- let us know if it doesn't! If it turns out that a capsid is sitting on a symmetry axis, Phaser will probably reject it because of an outrageous number of clashes. In that case, you should turn off the clash test, just look for one copy, and then examine the overlapped solution to see which part of the capsid is crystallographically unique. Good luck! Randy Read On Oct 22 2009, SIPPEL,KATHERINE H wrote:
Dear all,
I am currently trying to use AutoMR to do molecular replacement on an icosahedral virus capsid. It is a T=1 capsid so there are 60 copies of the monomer per capsid and based on the Matthews coefficient there are ~3 capsids in the unit cell. The search model is 99% identical (thank God) but I am unsure how to approach this.
Do I used the 60-mer as the model and search for three copies? Do I use a monomer for the model and search for 180 copies? Should I break the model down to smaller pieces (i.e. a 30-mer and copies=6, or 12-mer and copies=15)?
I would appreciate any help I can get on this one.
Thanks,
Katherine
-- SIPPEL,KATHERINE H Ph. D. candidate Department of Biochemistry and Molecular Biology College of Medicine University of Florida
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Hi Katherine,
Back when I did this with HBV I had one capsid per crystallographic AsU and I used Amore (pre-phaser or phenix). I searched with the icosohedral ASU looking for 60 copies, and was surprised how easily the solution fell out. If you use this strategy, you really just need one icos ASU per capsid and you can then expand the rest using standard icos symmetry.
I think the answer will be do what's easiest, and if it's 99% ID it should fall out pretty easily anyway. Bear in mind that depending on what you've done to these capsids the icos ASU's may have slightly re-oriented (in my case I had added a drug that kept the icos ASU identical but had tilted the whole thing relative to the plane of the capsid). This may also guide your strategy.
Good luck,
Christina
PS- Isn't Mavis around in Florida somewhere, or are you even in her lab? She and Rob are a great resource....
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From: "SIPPEL,KATHERINE H"
participants (3)
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Christina Bourne -
Randy J. Read -
SIPPEL,KATHERINE H