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Rapid Protein Side-Chain Packing via Tree Decomposition. Jinbo Xu email@example.com Department of Mathematics Computer Science and AI Lab MIT. Outline. Background Motivation Method Results. Protein Side-Chain Packing.
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Department of Mathematics
Computer Science and AI Lab
The picture is adapted from http://www.cs.ucdavis.edu/~koehl/ProModel/fillgap.html
Each residue has many possible side-chain positions.
Each possible position is called a rotamer.
Need to avoid atomic clashes.
Assume rotamer A(i) is assigned to residue i. The side-chain packing quality is measured by
The higher the occurring probability, the smaller the value
: distance between two atoms
Minimize the energy function to obtain the best side-chain packing.
Residue Interaction Graph
No previous algorithms exploit these features!
lTree Decomposition[Robertson & Seymour, 1986]
Greedy: minimum degree heuristic
XlSide-Chain Packing Algorithm
A tree decomposition rooted at Xr
The score of component Xi
The scores of subtree rooted at Xl
The score of subtree rooted at Xi
The scores of subtree rooted at Xj
Tested on the 180 proteins used by SCWRL 3.0.
Components with size ≤ 2 ignored.
Theoretical time complexity: <<
is the average number rotamers for each residue.
Five times faster on average, tested on 180 proteins used by SCWRL
Same prediction accuracy as SCWRL 3.0
CPU time (seconds)
A prediction is judged correct if its deviation from
the experimental value is within 40 degree.
An optimization problem admits a PTAS if given an error ε (0<ε<1),
there is a polynomial-time algorithm to obtain a solution close to
the optimal within a factor of (1±ε).
Chazelle et al. have proved that it is NP-complete to approximate this problem within a factor of O(N), without considering the geometric characteristics of a protein structure.
Give a novel tree-decomposition-based algorithm for protein side-chain prediction
Exploit the geometric feature of a protein structure
Efficient in practice
Theoretical bound of time complexity
Polynomial-time approximation scheme
Available at http://www.bioinformatics.uwaterloo.ca/~j3xu/SCATD.htm
Ming Li (Waterloo)
Bonnie Berger (MIT)
Tree width O(1)
Tree width O(k)
Partition the residue interaction graph to two parts
and do side-chain assignment separately
To obtain a good solution