a one dimensional string was thought of as a zero dimensional point particle because of how small it was, and the more advanced mathematics behind the theory of strings. And energy is not a mathematical construct, its a real thing. You can have pure energy. Energy and mass are the same thing...
Well I'm not really knowledgable about Brane Theories. I know a lot about string theory, but not so much about branes. However, it seems that your question is really dealing with the time dimension. Its interesting to think of multi-time dimensions, however, you cannot think of time in the same...