Bioinformatics Lab, Dept. of Biotechnology, Heritage Institute of Technology, Kolkata, India Summary Working with trajectories generated with Desmond and GROMACS molecular dynamics (MD) software can become quite inconvenient when simulations are extended multiple number of times with the same. Extended simulations allow Bioinformaticians to observe and interpret plots up to greater lengths of time and also do it at their own time of convenience when with lesser resources. To make this process simpler and easier, TrajectoryMergeAssist was created. It is a very handy and user-friendly GUI tool for Bioinformaticians to manage extended trajectories and finally merge all of them into a single trajectory with a series of steps and observations: With every gradual extended simulation, the user would like to view the resultant statistical plots starting from the first trajectory until the end of the second. The user would be eager to view the statistics of the same after the end of each extended simulation and that is when this tool becomes very useful. With further extended simulations, the user can use the combined trajectory obtained previously and merge it with the third and so on. The tool has been written in Python 2.7 and makes use of Tkinter, one of Python's own GUI programming toolkits. Another version has also been written in Python 3. Key Features Works with both the latest and older versions of Desmond Starting with Desmond 2018.1, a new Desmond script has been introduced and the earlier one has been deprecated for merging trajectories. TrajectoryMergeAssist checks for the same and proceeds accordingly, in order to support both the latest and earlier versions. Generates "-out.cms" file ready for use in Maestro Unlike versions prior to 2018.1, Desmond creates "merged.cms" files instead of "merged-out.cms", making it a requirement to manually rename it to the latter to make it ready for viewing on Maestro. TrajectoryMergeAssist also takes care of this by generating an "-out.cms" file instead of ".cms". Works with GROMACS ".xtc" files Added similar GUI support for GROMACS trajectories (".xtc" files). Easy Installation Download the installer. To install, just use a terminal and run: chmod +x tma_v2.1-setup.sh ./tma_v2.1-setup.sh The installer will also set the path for you. Run TrajectoryMergeAssist GUI with the following simple command: tma "tma_test_data.zip" has been included as test data on GitHub Steps to use TrajectoryMergeAssist i. Merging Desmond MD trajectories 1. Make sure you have the following required input files and trajectories:     a. The "-out.cms" file     b. The first trajectory directory (name ends with "_trj")     c. The second trajectory directory from an extended Desmond MD simulation 2.  It is recommended to work with the above files from a location like:          /home/username/directory/ 3.  Navigate to the directory on a terminal window and run:     tma or   tma-py3 -- For Python3 Only 4.  Select the "-out.cms" file 5.  Navigate to the two trajectory directories ending with "_trj" 6.  The 3 choices will be visible in the background terminal so that the selections can be confirmed. 7.  Click on "Merge Desmond Trajectories" 8.  Wait until the "...Done!" message 9.  The new merged trajectory along-with the new "-out.cms" file can be found in the same working directory ii. Merging GROMACS MD trajectories 1. Make sure you have the following required input trajectory files:     a. The first trajectory file (name ends with ".xtc")     b. The second trajectory file from an extended GROMACS MD simulation 2.  It is recommended to work with the above files from a location like:          /home/username/directory/ 3.  Navigate to the directory on a terminal window and run:     tma or   tma-py3 -- For Python3 Only 4.  Choose to the two trajectory files ending with ".xtc" 5.  The 2 choices will be visible in the background terminal so that the selections can be confirmed. 6.  Click on "Merge GROMACS Trajectories" 7.  Wait until the "...Done!" message 8.  The new merged trajectory (".xtc" file) can be found in the same working directory.   References Robert T. McGibbon, Matthew P. Harrigan, Kyle A. Beauchamp. 2015. “MDTraj: A Modern Open Library for the Analysis of Molecular Dynamics Trajectories.” Biophysical Journal 109 (October). Elsevier:1528–32. https://doi.org/10.1016/j.bpj.2015.08.015. Kevin J. Bowers, Huafeng Xu, Edmond Chow. 2006. “Scalable Algorithms for Molecular Dynamics Simulations on Commodity Clusters.” In Proceedings of the 2006 Acm/Ieee Conference on Supercomputing. SC ’06. Tampa, Florida, USA: CiteSeerx. https://citeseerx.ist.psu.edu/viewdoc/citations?doi=10.1.1.98.2121. D. E. Shaw Research, New York, LLC. n.d. “D. E. Shaw Research | Desmond.” https://www.deshawresearch.com/resources_desmond.html. Schrödinger, New York, LLC. n.d. “Schrödinger | Maestro.” https://www.schrodinger.com/maestro. Gmx trjcat - GROMACS 2019.1 documentation. (n.d.). Retrieved from http://manual.gromacs.org/current/onlinehelp/gmx-trjcat.html