Identification and organization of the components in the isolated microvillus cytoskeleton

Abstract

We have examined the effects of ATP and deoxycholate (DOC) on the cytoskeletal organization of Triton-demembranated microvilli (MV) isolated from chicken intestine brush borders. Isolated MV are composed of a core of tightly bundled microfilaments from which arms project laterally to the plasma membrane with a 33-nm periodicity. These lateral arms spiral around the core microfilaments as a helix with a 25° pitch. Demembranated MV consist of four polypeptides with mol wt of 110,000, 95,000, 68,000, and 42,000, present in molar ratios of 1.1:1.6:1.3:10.0. After addition of 50 μM ATP and 0.1 mM Mg++, the cytoskeletons are organized as a tight bundle of microfilaments from which lateral arms are missing. In thse ATP treated cytoskeletons, the 110 kdalton polypeptide is reduced in amount and the 95,000, 68,000 and 42,000 polypeptides are present in a 1.3:1.2:10.0 ratio. In contrast, after incubation with 0.5% DOC, the core microfilaments are no longer tightly bundled yet the lateral arms remain attached with a distinct 33-nm periodicity. These DOC-treated cytoskeletons are depleted of the 95,000 and 68,000 polypeptides and are composed of the 110,000 and 42,000 polypeptides in a 2:10 molar ratio. These results suggest that the microfilaments are associated into a core bundle by the 95- and 68-kdalton polypeptides and from this core bundle project the lateral arms composed of the 110-kdalton polypeptide.