A team is at first a group of individuals with own motivations and interests. They come together because there is a common task, target (a vision) that has to be clear, unambiguous and at best fully accepted by all.
The team members individually have to understand what their contribution to the common vision is (their role) but also that they are now part of a new human community. So their accountability is two-sided: for their role and for the community.
The PM has to ensure that both sides are in place:
1. a commonly understood set of roles and interfaces. The coverage of roles should not leave gaps of required capabilities. The interfaces or reporting lines are needed for efficient communication.
2. a Community with a sense of purpose (derived from the vision), boundaries and a common culture (beliefs, rites, signs etc) to foster belonging, trust and synergy.
In my experience building the community is more important than creating the structure. Both are needed to create a high performance team.