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In structural biology, a beta-propeller is a type of all-β protein architecture characterized by 4 to 8 blade-shaped beta sheets arranged toroidally around a central axis. Each sheet typically has four antiparallel β-strands twisted so that the first and fourth strands are almost perpendicular to each other. The enzyme's active site is often found in the cleft formed in the center of the propeller by loops connecting the successive four-sheet motifs. Murzin proposed a geometric model to describe the structural principles of the beta propeller. According to this model the seven bladed propeller was the most favoured arrangement in geometric terms. ==Examples== The influenza virus protein viral neuraminidase is a six-bladed beta-propeller protein whose active form is a tetramer. It is one of two proteins present in the viral envelope and catalyzes the cleavage of sialic acid moieties from cell-membrane proteins to aid in the targeting of newly produced virions to previously uninfected cells. The plant UV-B sensing protein UVR8 is a seven-bladed propeller which is dimeric until absorption of UV-B light, which causes dissociation. WD40 repeats, also known as beta-transducin repeats, are short fragments found primarily in eukaryotes. They are often assembled in 4 to 16 repeated units to form a structural domain critical for protein-protein interactions. A beta-propeller is a critical component of LDLR (low density lipoprotein receptor) and aids in a pH based conformational change. At neutral pH the LDLR receptor is in an extended linear conformation and can bind ligands (PCSK9). At acidic pH the linear conformation changes to a hairpin structure such that ligand binding sites bind to the beta-propeller, preventing ligand binding. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Beta-propeller」の詳細全文を読む スポンサード リンク
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