To determine the functions of the proteins found in the protein interactome as shown on the previous page, scientists for this experiment used data sets of other strains that would have proteins that were orthologous to the proteins found in S. pneumoniae. A protein that is orthologous to another means that both proteins have deviated and evolved from a common ancestor. What this information implies is that ortholog proteins may include similar if not identical functions and interactions. For example, if Protein A and Protein B are orthologs and Protein A is known to have transcriptional responsibilities, then Protein B would most likely include transcription functions as well.

The derived proteins interactions came from the following strains for this study: C. jejuni, M. loti, Synechocystis, B. subtilis, T. pallidum, H. pylori, E. coli, and M. tuberculosis.

These strain interactomes were observed to determine and create a meta-interactome for S. pneumoniae. This meta-interactome consists of the union of all interactions from other bacteria that were orthologous with S. pneumoniae.

The graph to the right shows the number of protein-protein interactions (as labeled on the x-axis) that were found in the other orthologous strains. Orange identifies the count of proteins that have S. pneumoniae orthologs.

Fig. 5: Comparison of interactomes of orthologous bacteria. The number of protein-protein interactions (PPI) are shown between the strains of bacteria with S. pneumoniae
 

SP_1876 is the protein that was observed in S. pneumoniae and this was chosen as it is identified as a protein with an unknown function. The list to the right includes all proteins that interact with this unknown function that was found both in the yeast two-hybrid method and in the created meta-interactome. The following proteins are identified to have the following functions: replication, translation, cell cycle, transcription, nucleotide transport, posttranslational modification, signal transduction, transcription, and inorganic ion transport.

The bolded proteins were found with the yeast two-hybrid dataset and the others were found with the created meta-interactome. It was discovered that the majority of the functions in the protein network designed for S. pneumoniae were responsible for transcription processes.

Table 1. Table of interactions with S. pneumoniae bacterial strain. EXPLAIN TABLE HERE