Proteins of human placental microvilli: I. Cytoskeletal proteins

Microvilli isolated from the syncytiotrophoblast surface of the human term placenta were separated into two fractions, one of which contained microvilli lacking a visible cytoskeleton on electron microscopy. One- and two-dimensional electrophoresis showed that a number of proteins were present in reduced amounts in the fraction lacking a visible core structure. The possibility that these proteins were cytoskeletal components was investigated by further electrophoretic studies in conjunction with 125I labelling of proteins of intact and disrupted microvillous vesicles, digestion of external proteins with immobilized, insoluble trypsin, and selective solubilization of plasma membrane proteins by Triton X-100. From the results of these studies, eight proteins of molecular weights 103 000, 80 000, 70 000, 69 000, 43 000, 36 000, 25 000 and 18 000 were tentatively assigned to the cytoskeleton. The differences between our findings for the cytoskeletal proteins of human placental microvilli and the results reported by others for the well-studied cytoskeletal proteins of the intestinal microvilli of the rat are likely to reflect differences in structure and function of the microvilli from the two sources.