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.
I was thinking about whether proteins playing the same role in a pathway will have similar structure properties (like size of protein, protein binding sites, and so on). I am not sure whether this is a valid question. Some proteins could be activator, inhibitor, or substrate.
The pathway common website is really great. The annotation of edges could be treated like the role for the relationship. But, for here, mostly are "changes the state" and this is only for genes.