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Glutton (A tool for Protein Chemical Shift - Structure Analysis)
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alt text Figure 1. Side-by-side comparison of the Phi and Psi angle distributions based on 10,000 structures obtained from 10-us MD simulations(left) and Glutton (right) for ALA-49 in NCBD.


Please take 5 minutes to read this brief readme file before running the Glutton script.

Part 1 of 4. Introduction of Glutton

    The Glutton database and a complementary python script are developed for constructing structure 
    ensembles solely based on backbone chemical shift data for flexible proteins.
    The Glutton database that we have developed is specifically designed to fill a void
    currently existing in the bioinformatics tools for the structural analysis of intrinsically
    disordered proteins (IDPs) based on experimental information, namely Nuclear Magnetic Resonance (NMR). 
    Our Glutton database contains both chemical shifts and their corresponding structural information 
    for a total of 5,270 proteins. The Glutton database is organized hierarchically in three tiers
    (levels of resolution) that permit customization of the database for specific applications: 
    for calculations of structural ensembles of IDPs, or for determination and prediction of well-folded 
    protein structures. And, most importantly, Glutton interprets chemical shifts as ensemble 
    averages, and thus calculates conformational distributions from chemical shift datasets. 
    These distributions permit the straightforward determination of a maximally broad structural 
    ensemble consistent with the data, and thus it optimizes sampling of the conformational space that is
    available to the IDP as shown in the above plot. These ensembles provide a realistic description
    of the conformational heterogeneity and structural propensities of IDPs, but they can also be used 
    as starting points for the refinement of protein structure determination (adding additional 
    experimental information) or protein prediction (incorporating a molecular force-field).

Part 2 of 4. Use Glutton script to generate structure ensembles based on chemical shifts or vice versa.

    Step1. Put database files (LEVEL*.dat), and input.txt files in the same folder.

    Step2. If there are no subfolders named "cs" and "PDBOUT" within this folder, create them before 
            running the Glutton script.

    Step3. Put the input chemical shift file (in NMRSTAR 3.0 format) in the subfolder "cs" or pdb file in subfolder "pdb"

    Step4. Change the input.txt to set parameters to determine the characteristics of the structure 
    ensemble to be generated.

            bmr15398.str   # name of the input chemical shift file in cs folder
            2              # LEVEL of the database, 1 - high-resolution; 2 - medium-resolution; 3 - low-resolution 
            200            # Number of structures to be generated (when predicting cs from a structure, set it to 1)
            0.5            # the selected width of the chemical shift distribution to derive statistical distributions (or the phi/psi angle range if predicting cs from a structure)
            1              # 0 - Output all Phi and Psi angles before size exclusion; 1 - output Phi and Psi angles used in all the outputed structures
            1              # 0 - predict chemical shifts based on PDB structure; 1 - predict strcutures based on chemical shifts

    NOTE: if the available data are insufficient to generate distributions, you can either: 
    [1]. use the low-resolution database - LEVEL3;            
    [2]. increase the selected width of the chemical shift distribution. 
    [3]. Output Phi and Psi angle files are named "PhiAngles.txt" and "PsiAngles.txt". Each row contains all
         the generated angles corresponding to one residue.

    Step5. Use the following command to run the Glutton script:


    NOTE: Example input files for Cs to structure is "input_cs2str_ncbd.txt" and for structure to CS is
     "input_str2cs_ncbd.txt". To use anyone of them as input file for Glutton, please change the file name
     to "input.txt" and put in the same folder as

Part 3 of 4. Python libraries needed to run this script

    The Glutton script has been tested using the Anaconda python distribution version 3.6. 
    The Anaconda python package can be downloaded for free from:
    The compatibility of the Glutton script with Python version 2.7 has NOT been evaluated. If you are using the 
    default python in linux, you are most likely using python version 2.7. You will have to manually specify 
    the python interpreter as:
    If you use the default python in Linux and don't have the pip command, you will need to install pip 
    as follows:
            sudo apt install python3-pip (Ubuntu)
            sudo yum install python3-pip (centos/redhat) - not tested

    The python libraries needed to run Glutton script are:

    [1]. Install Biopython

            conda install biopython (or use "pip install biopython")

    Biopython webpage:

    [2]. Install PeptideBuilder

            pip3 install PeptideBuilder

    PeptideBuilder webpage:

    M. Z. Tien, D. K. Sydykova, A. G. Meyer, C. O. Wilke (2013). PeptideBuilder:
    A simple Python library to generate model peptides. PeerJ 1:e80.

    [3]. Install nmrstarlib
            pip3 install nmrstarlib

    nmrstarlib webpage:        

    [4]. Install other python libraries such as numpy, pandas if you don't have them.
            pip3 install numpy pandas

Part 4 of 4. Protein Chemical Shift - Structure Database (Glutton database)

    All database files 

            LEVEL1_ALL_20180116.dat  (high-resolution)

            LEVEL2_ALL_20180116.dat  (medium-resolution)

            LEVEL3_ALL_20180116.dat  (low-resolution)

    are in csv format. 

    Each row represents a single residue, and the meaning of each column is as follows:

    column 1: residue type (one letter code)

    column 2: the chemical shift value of the H on the backbone N

    column 3: the chemical shift value of the backbone N

    column 4: the chemical shift value of the H on the backbone C_Alpha

    column 5: the chemical shift value of the backbone C_Alpha

    column 6: the chemical shift value of the backbone C'

    column 7: Secondary structure type of this residue

    column 8: Phi angle of this residue

    column 9: Psi angle of this residue

       NOTE: if the chemical shift value of an atom is not available, Glutton sets it as 9999.0.

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