ABC proteins

Purdue Biologists Clarify How A Cellular 'Spacecraft' Opens Its Airlock: "ABC proteins function like tiny tweezers and are powered by ATP, a chemical that animal cells use for energy. When ATP causes the tweezers to squeeze shut, the membrane proteins open to reveal a small cavity that can hold a nutrient or other substance the cell requires from the outside. Once the nutrient is in place, the cell uses water to break down the ATP, signaling the 'tweezers' to relax, closing the membrane protein gate and capturing the nutrient. Lastly, the membrane protein releases the nutrient into the cell's interior."