• Tutorials
• The Network page
• The Protein page
• The Interaction page
• Format of the downloadable files
• Interactome3D RESTful API
• Frequently asked question

Here you can find a series of very short video tutorials that will guide you through the basic functionalities of the Interactome3D web service.

Overview	Submit your data and check the results	Browse Interactome3D pre-built datasets
Query with a list of proteins	Download Interactome3D data

You can also follow our step-by-step tutorials:

• Submit your data and check the results
• Browse Interactome3D pre-built datasets
• Query Interactome3D with a list of proteins
• Download Interactome3D data

The Network page allows the user to get an overview of the interaction network together with the available structural data for both proteins and interactions and to access the details about these data by clicking on the nodes or on the edges of the network.

The Protein page displays details about the protein, including all the available structural data and allows the user to preview and download the structures and models.

The Interaction page displays details about the interaction, including all the available structural data and allows the user to preview and download the structures and to access external experimental evidences for the interaction.

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Structures and models visualization pane A graphical pane displays the parts of the two interactors that are present in the different interaction structures/models. Every line represents a different structure/model and the colored bars indicate which portion of the protein sequence is modeled in the structure. The colors indicate the type of the structure/model: green for experimental structures, orange for homology models from global templates and red for models from domain-domain templates. The intensity of the color depends on the sequence identity between the template and the target protein. For every interaction there can be multiple structures/models. Different structures/models for an interaction can span different portions of the two proteins and show different interaction modes. A quick look to this pane will help you in distinguishing between different structural modes of interactions. Any interaction can have only one of the different types of structural data (experimental structures, models from global templates and models from domain-domain structural templates). This means that, if an interaction has experimental structural data, no homology model is produced for it. If there is no experimental structure but there are global templates available than only the models from the gloabal templates are produced and not the models from domain-domain templates. If neither experimental structures nor global templates are available then Interactome3D tries to model the interaction on the basis of the available domain-domain structural templates. The modeling strategy adopted by Interactome3D is better described in the Interactome3D publication (see the references page). Nevertheless, we would like to spend a few words here on the strategy used for the selection of domain-domain structural templates when multiple templates are available. When modeling an interaction using domain-domain structural templates it is possible that the domain assignment to the two proteins allows for multiple possible domain-domain pairs mediating the interaction. For example, if the star, square, circle and triangle in the previous image all represent different domains then there are at least 4 possible domain-domain pairs that mediate the interaction. In order to select one structural template for the interaction we need to decide which domain-domain template is the most likely to mediate the interaction. This selection, in Interactome3D, is done using a strategy based on the network of preferred domain-domain interaction pairs observed in the PDB, as described in the work of Itzhaki et al. (Itzhazi, Akiva & Margalit, Bioinformatics 26:2564-2570, 2010). Given all the possible domain-domain pairs we build the network of preference between them and we select the one that dominates over the others. Please refer to the original publication for a description of how the network of preference is built. Then we select in 3did all the structural templates corresponding to this particular domain-domain pair and we take the template corresponding to the most numerous topology in 3did. There is still the possibility that no domain-domain pair dominates over the others. This happens when the network of preference forms a cycle. In this case we select all of them and we take one template for every domain-domain pair. The name of the domains used in the modeling of the interaction can be found in the table of structures/models for the interaction (identified by the number (3) in the image). By hovering over the lines in this pane you get a description of the PDB entry from which the structure or the model were taken. By clicking you can select the corresponding structure in the table below.

Data for pre-built and user datasets calculated by Interactome3D can be downloaded for offline analysis. When you click on the download button you will be taken to a page where you can download two different sets of results:

• Complete set: This set contains all the structures and models that have been collected and generated for both proteins and interactions
• Representative set: This set contains only the top ranked structures and models that have been collected and generated for both proteins and interactions

Both in the complete and in the representative set, the same protein can have more than one structure or model. Structures for proteins and interactions are collected from the Protein Data Bank (PDB) while homology models for single proteins are collected from Modbase and homology models for interactions are generated using Modeller on structural templates extracted either from PDB biological unit files or domain-domain structural templates downloaded from 3did.

Stuctures and models for the same protein or interaction are ranked based on several criteria. You can see the ranking of the structures in the table contained in the pages showing details for proteins and interactions when browsing the results on-line. The ranking has the form n.m where n is the major rank index while m is the minor one. Structures with lower rank major index are, in general, of a higher quality then structures with a higher rank major index. The criteria used to rank structures and models for single proteins are the following:

• Complete experimental structures are ranked first in the list and in order of decreasing coverage. A structure is considered to be complete if it covers more than 80% of the protein sequence length. A complete experimental structure always has the rank minor index equal to 0.
• Complete homology models are ranked just after complete experimental structures in decreasing order of sequence identity of the template to the target. A complete homology model always has the rank minor index equal to 0.
• Partial experimental structures and homology models are ranked after complete homology models. In this case Interactome3D tries to group together structures that cover, together, the largest portion of the protein sequence length. The different groups are generated by a greedy algorithm that takes into consideration the structures sorted by decreasing values of the following scoring function:
  
  which takes into account the coverage of the structure and the sequence identity of the template to the target protein. The parameter alpha is set to 0.95 from empirical observations. Every group of structures/models is assigned the same rank major number and different rank minor numbers in order of starting residue of the structure.

When creating the representative set only the structures/models with rank major index equal to 1 are retained. This means that also in the representative set we can have more than one structure for the same protein. This happens when a protein only has structures/models with a coverage lower than 80%. In this case, as described before, the program selects a group of (potentially) overlapping structures/models that together span the largest portion of the protein sequence.

The ranking for interaction structures/models is simpler:

• Experimental structures are ranked first in the list and in decreasing order of the values of the following score function
  
  where the sequence identity and coverage of the two interacting proteins are taken into consideration. The parameter alpha is set to 0.95 from empirical observations.
• Homology models from generic PDB templates are ranked after the experimental structures in decreasing order of the values of the previous score function
• Homology models from domain-domain structural templates are ranked at the end of the list in decreasing order of the values of the previous score function

In the case of interactions the representative dataset contains only one structure per interaction, the one with rank major number equal to 1. The rank minor index for interaction structures/models is always equal to 0.

For every set of results (complete and representative) there are two tables (proteins.dat and interactions.dat) summarizing the structures and models collected and generated for proteins and interactions and two sets of tarballs (proteins_xxx.tgz and interactions_xxx.tgz) containing the corresponding PDB files. Every tarball contains a maximum of 500 structures. If the dataset contains more than 500 structures they are splitted into different tarballs named with an increasing numbering scheme.

The table proteins.dat contains, for every structure, the following columns:

The table interactions.dat contains, for every structure, the following columns:

Feel free to contact us if you have any question about the format of the downloaded data and how to use them.

The data contained in Interactome3D can be accessed programmatically through a RESTful interface. The interface is available through the 'api' subfolder and the URL of the request is encoded as in the following examples:

https://interactome3d.irbbarcelona.org/api/getProteinStructures?uniprot_ac=A0A5B9 https://interactome3d.irbbarcelona.org/api/getInteractionStructures?queryProt1=A0A5B9&queryProt2=P01848

The following functions are available:

• getUniprotACs It returns the Uniprot ACs of all the proteins contained in one of the precalculated datasets in Interactome3D. It takes no parameters and returns the list of Uniprot ACs as raw text, separated by newlines.
• getProteinStructures It returns the list of structures for one protein . It takes only one parameter:
  • uniprot_ac The Uniprot AC of the protein of interest
  The function returns an XML encoded string which contains a main element named interactome3D having an attribute version that corresponds to the current version of Interactome3D. This element contains a child protein_structure_list which, in turn, containes many protein_structure elements (one for every structure). The children of each protein_structure element correspond to the columns in the file proteins.dat file.
• getInteractionStructures It returns the list of structures for one interaction. It takes two parameters:
  • queryProt1 The Uniprot AC of the first protein
  • queryProt2 The Uniprot AC of the second protein
  The function returns an XML encoded string which contains a main element named interactome3D having an attribute version that corresponds to the current version of Interactome3D. This element contains a child interaction_structure_list which, in turn, containes many interaction_structure elements (one for every structure). The children of each interaction_structure element correspond to the columns in the file interactions.dat file.
• getPdbFile It returns the contents of one of the PDB files contained in Interactome3D. It takes two parameters:
  • filename The name of the PDB file as contained in the proteins.dat or interactions.dat file or returned by one of the previous APIs
  • type Can be either protein or interaction depending if you want to fetch the PDB file of a single protein or interaction.
  The function returns an XML encoded string which contains a main element named interactome3D having an attribute version that corresponds to the current version of Interactome3D. This element contains a child pdb_file_list which, in turn, containes one pdb_file element (one for every structure). This element contains one filename child containing the name of the PDB file and one contents child containing the actual PDB file, line by line.
• getVersion It returns the current version of Interactome3D, as raw text.

• How frequently is Interactome3D updated?
• What is the difference between complete structures, complete models and partial models for proteins?
• If I query Interactome3D with proteins X, Y and Z the answer includes proteins X, T, W but no Y and no Z. Why is the set of query proteins so different from the answer?
• If I query Interactome3D with proteins A, B and C the answer includes many more proteins. How can I restrict the results to only the proteins in specified in the query?
• What is the meaning of the blue bar (available for docking) in the interactions chart in the results page?

How frequently is Interactome3D updated?

Twice a year, every 6 months.

What is the difference between complete structures, complete models and partial models for proteins?

Structures and models are considered to be complete if they span at least 80% of the length of the protein sequence. Otherwise they are classified as partial.

If I query Interactome3D with proteins X, Y and Z the answer includes proteins X, T, W but no Y and no Z. Why is the set of query proteins so different from the answer?

The pre-built datasets contained in Interactome3D are composed of binary interactions available in public Databases (Intact, MINT, HPRD, BIND, etc...) and the corresponding structural data available in the PDB or that can be modeled by homology. When the user queries Interactome3D with a set proteins the result of the query will be all the interactions involving at least one of the proteins in the query set. In the case of the example Interactome3D contains experimentally identified binary interactions only for protein X (interacting with proteins T and W). No interactions have been discovered (or at least are not available in the public databases that Interactome3D uses) for the other two query proteins (Y and Z). For this reason the answer will include the proteins that are known to interact with X (T and W) but not the query proteins Y and Z.

If I query Interactome3D with proteins A, B and C the answer includes many more proteins. How can I restrict the results to only the proteins in specified in the query?

By default, Interactome3D returns all the interactions involving any protein in the query list. If you want to only display interactions between any two proteins in your query list you can check the option "Only show the proteins in the list" below the input box in the home page. If you do so, the results will include only the interactions for which both the interactors are in your query list. This is particularly useful if you want to visualize the experimentally validated interactions between components of the same complex.

What is the meaning of the blue bar (available for docking) in the interactions chart in the results page?

For those interactions that do not have a structure or a model there is still hope, provided that we have a structure or a model for both the single interactors. These are exactly the interactions that correspond to the blue portion of the bar. In these cases, we can apply computational protein-protein docking in order to try to predict the structure of the interaction.
The current version of Interactome3D does not automatically apply docking to those cases but we have an internal pipeline that can be used for running docking experiments in a high-throughput manner on all the interactions having structures/models for both the unbound proteins.
Due to the computational complexity of the problem we will take into consideration the possibility of applying such protocol on a collaboration basis.