Proteomic Analysis of Apical Microvillous Membranes of Syncytiotrophoblast Cells Reveals A High Degree of Similarity with Lipid Rafts

Brush borders (microvilli) are cell membrane
specialized structures that function mainly as high-throughput absortive/secretory areas. It has been well-established that brush borders are particularly rich in
membrane lipids characteristic to lipid rafts. Here, we
report 57 proteins identified from microvillous membranes (MVM) isolated from human syncytiotrophoblast
cells using an experimental method that avoids the use
of nonionic detergents. About 60% of the proteins reported here have been described previously as lipid-raft
specific. Well-known lipid raft-markers such as Annexin
A2 and alkaline phosphatase were identified. Cytoskeleton
structural constituents and proteins related with the
control and modulation of the cytoskeletal architecture as
well as the regulation of the interaction of cytoskeletal
constituents with the cell membrane and particularly with
lipid raft domains were found (Ezrin, IQGAP1 and 2,
EBP50). Other proteins identified include signal transduction molecules, such as Ras-related protein Rab-1B and
Rab-7, and ADP-ribosylation factor 1. Several proteins
harbor putative post-translational modifications that favor
its localization in the lipid-raft environment, such as GPI
(alkaline phosphatase and 5'-nucleotidase) and myristoylation (BASP1 and MARCKS). On the whole, this extensive description demonstrates from the protein composition point of view that brush border membranes are
indeed highly enriched in lipid raft microdomains.
Keywords: lipid raft • brush border • syncytiotrophoblast •
multidimensional chromatography-nano ESI−MS/MS • in-solution digestion