Demonstration of three distinct calcium-binding sites in villin, a modulator of actin assembly.

摘要: Villin, a Ca2+-modulated F-actin-binding protein (95,000 daltons) present in microvillus core filament bundles, has been shown to contain multiple Ca2+-binding sites. 45Ca Hummel-Dreyer chromatography reveals the presence of two rapidly exchanging sites with an apparent dissociation constant, Kd, equal 4.6 X 10(-6) M. Use proteolytically separable domains molecule revealed that one site is located on 90,000-dalton (apparent Kd = 3.5 M) while second provided by 8,800-dalton headpiece fragment 7.4 M). In addition villin displays further very slowly or nonexchangeable high affinity site, which situated domain. Secondary structural predictions and comparison amino acid sequence other known proteins indicates region suggestive although seems not exhibit classical "EF-hand" structure.