valkude torukujuliseks struktuuriks kokkukeerdunud β-kiht, milles esimene kiud on seotud viimasega vesiniksideme abil, A large beta-sheet that twists and coils to form a closed structure in which the first strand is hydrogen bonded to the last. Beta-strands in beta-barrels are typically arranged in an antiparallel fashion. Appear in membrane porines and cytosolic export complexes, such as TOC complex in chloroplasts.