Assertion: membrane protein | /r/CapableOf | serve as channel
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Source sentences:
text: A protein may be classified based on its form and main functions: it can be a globular protein like most enzymes, a fibrous protein (with a structural role, such as collagen, keratin, etc.), or a membrane protein that serves as a receptor or a channel (where a polar or a charged molecule can move into the cell across the cell membrane).