Villin: The major microfilament-associated protein of the intestinal microvillus

Publisher Website
Google Scholar
Abstract
The major protein associated with actin in the microfilament core of [chicken] intestinal microvilli was purified. This protein, which was named villin, has a polypeptide MW of .apprx. 95,000. Villin may be the microvillus crossfilament protein that links the microfilament core laterally down its length to the cytoplasmic side of the plasma membrane. EM shows that crossfilaments stay attached to isolated membrane-free microvillus cores. Calculation of the expected abundance of the crossfilament protein shows that only villin is present in sufficient quantity to account for these structures. Decoration of microvillus cores by antibodies to either actin or villin, followed by ferritin-labeled 2nd antibody in a sandwich procedure, results in specific labeling of the cores in both cases. The antivillin decoration gives rise to a greater increase in diameter, in agreement with a model in which villin projects from the F-actin microfilament core. Villin is distinct from .alpha.-actinin, a protein suggested to be involved in membrane anchorage of microfilaments in non-muscle cells. The 2 proteins differ in MW. Specific antibodies against villin and .alpha.-actinin show no immunological crossreactivity. Immunofluorescence microscopy reveals that villin is located in the microvilli of the brush border whereas .alpha.-actinin is absent from the microvilli but is found in the terminal web. Villin is not found in microfilament bundles of tissue culture cells, which are rich in .alpha.-actinin. Villin and .alpha.-actinin appear to be immunologically and functionally different proteins.