As data sources, you can use any number of public databases containing human protein-protein interactions. For a more exhaustive graph of interactions, you could use iRefIndex which combines interactions from several databases. As for the Matlab part, Matlab is not very much used in bioinformatics so there may not be ready-to-use tools for dealing with protein-protein interactions. If Matlab has tools for dealing with graphs, you could try using them and see how far they get you. Otherwise, I think you'll have to code how to extract the interactions you want yourself.