Mutlinational corporations (MNCs) and international institutions are two very different things.
An MNC is an entity with a profit motive. Think Exxon or GE. They're in business to make money for their shareholders. It's that simple.
International institutions are responsible for the rules and norms that international businesses operate under. A great example would be the World Trade Organization (WTO). It creates standards and incentivizes free trade by interacting with governments, non-governmental organizations, and businesses. It has no profit motive; it has a separate mission. Other examples might by the International Monetary Fund (IMF) or Energy Industry Transparency Initiative (EITI). These are also called non-governematal organizations (NGOs).
There could be overlap in these two as some MNCs pursue advocacy internationally in supportof CSR initiatives or for other reasons. For instance, it would be unrealistic to think that BP is not going to have a stake in climate change negotiations or that Proctor and Gamble isn't interested in non-tariff barriers in Asia. But, in sum, the two are very different and should not be conflated.