Clustering ligand conformations using cartesian PCA ===================================================== In this example, conformation of ligands were clustered with respect to receptor. At first, PCA was performed using atom-coordinates (cPCA), and subsequently, projections on eigenvectors were used as the features Atom-coordinates PCA --------------------- 1. **Covariance, eigenvector and eigenvalue caculcations** .. code-block:: bash echo 13 14 | gmx covar -s input-files/input.tpr -f input-files/trajectory.xtc -n input-files/input.ndx Here, ``13`` is index group of receptor atoms, which were used for superposition by least-square fitting. ``14`` is index group of ligand without any hydrogen atoms. Above command generated ``eigenvec.trr`` and ``eigenval.xvg`` files. ``eigenvec.trr`` is necessary in next command as input. 2. **Projections on eigenvectors** .. code-block:: bash echo 13 14 | gmx anaeig -s input-files/input.tpr -f input-files/trajectory.xtc -n input-files/input.ndx -proj -first 1 -last 20 In the above command, ``-v eigenvec.trr`` was used by default and eigenvectors were read from this file. A new output file ``proj.xvg`` is generated containing projections on first 20 eigenvectors. This file is used as an input file in ``gmx_clusterByFeatures``. Clustering ----------- .. code-block:: bash echo 0 14 13 | gmx_clusterByFeatures cluster -s input-files/input.tpr -f input-files/trajectory.xtc -n input-files/input.ndx \ -feat proj.xvg -method kmeans -nfeature 20 -cmetric ssr-sst -ncluster 15 \ -fit2central -sort features -cpdb clustered-trajs/central.pdb \ -fout clustered-trajs/cluster.xtc -plot pca_cluster.png\ K-means clustering was used with maximum number of 15 clusters (``-ncluster 15``). It means, clustering were performed 15 times, and in each iteration, starting from two, one more cluster was generated. Subsequently, 9 clusters were accepted as final clusters using change in SSR/SST ratio (``-cmetric ssr-sst`` and ``-ssrchange 2``) .. note:: Check carefully order of index groups selected in the above command. **a.** First index group - output in central structures and clustered trajectories **b.** Second index group - clustering group, here it is ligand without hydrogen atoms **c.** Third group - Used for superposition by least-square fitting. Outputs -------- **Central structures of each cluster:** .. code-block:: bash Cluster-ID Central Frame Total Frames 1 45447 19639 2 51211 15441 3 36523 10488 4 63595 9101 5 70685 6909 6 41378 6157 7 3166 5891 8 21937 4756 9 7755 2166 **RMSD (nm) between central structures:** .. code-block:: bash c1 c2 c3 c4 c5 c6 c7 c8 c9 0.000 0.292 0.701 0.444 0.484 0.498 1.076 0.411 0.883 0.292 0.000 0.684 0.428 0.418 0.552 1.063 0.439 0.844 0.701 0.684 0.000 0.834 0.574 0.360 0.860 0.588 0.812 0.444 0.428 0.834 0.000 0.571 0.705 0.940 0.733 0.763 0.484 0.418 0.574 0.571 0.000 0.351 0.947 0.670 0.961 0.498 0.552 0.360 0.705 0.351 0.000 0.959 0.548 0.967 1.076 1.063 0.860 0.940 0.947 0.959 0.000 1.165 0.614 0.411 0.439 0.588 0.733 0.670 0.548 1.165 0.000 0.890 0.883 0.844 0.812 0.763 0.961 0.967 0.614 0.890 0.000 **Output files generated:** a. ``-g cluster.log`` : log output containing information about the clusters. b. ``-clid clid.xvg`` : Cluster-id as a function of time. c. ``-fout clustered-trajs/cluster.xtc`` : 9 clustered trajectories were extracted with name cluster_c{ID}.xtc d. ``-cpdb clustered-trajs/central.pdb`` : 9 central structures PDB files were extracted with name central_c{ID}.pdb e. ``-plot pca_cluster.png`` : Plots of feature-vs-feature with different colors as clusters and central structure. This plot can be used for visual inspection of clustering.