We can easily find whether the protein is in certain pathway. But, is there any role annotation of proteins in pathways? Because, one protein may act as different roles in different pathways. This is probably related to semantic net for the biological process within a cell or system biology.
Would pathwaycommmons.org webservices would help?
Also would you elaborate a bit more on your use case? What do you expect in terms of the "role annotation" ? A controlled vocabulary term? What would be some example terms?
What you are exploring is a simplified view, geared toward mostly genomic use-cases - PC contains detailed information about the actual reactions between proteins. You can use Chibe to fully explore them: http://www.biomedcentral.com/1471-2164/15/642
As with the protein structure properties I am not sure about the roles but phosphorylation sites of different proteins tend to have some property similarities but the signal is not very strong in my experience.