Comprehensive proteome analysis of brush border membrane fraction of ileum of ezrin knockdown mice.

: Ezrin is an actin binding protein which cross-links membrane proteins with cytoskeleton directly or indirectly via PDZ domain-containing scaffold proteins. It is mainly expressed at the brush border membrane (BBM) of gastrointestinal tracts, and is involved in the construction of microvilli structure and the functional expression of membrane protein complexes at the cell surface. To precisely study the roles of ezrin on the expression of membrane proteins at the cell surface, here we prepared the BBM fractions of ileums from the wild-type and ezrin-knockdown (Vil2(kd/kd)) mice, analyzed them by mass spectrometry, and compared their proteomic patterns. Totally 313 proteins were identified in the BBM fractions. Several transport proteins, cytoskeleton-associated proteins, and trafficking proteins were up- or down-regulated in the BBM fraction of the ileum in the Vil2(kd/kd) mice. Among them, the expressions of i) Na(+)/H(+) exchanger regulatory factor 1 (a PDZ domain-containing scaffold protein), ii) sodium monocarboxylate transporter 1, which contains a PDZ domain-binding motif at their carboxy-terminal, and iii) chloride intracellular channel protein 5 were down-regulated at the BBM fraction of the ileum in the Vil2(kd/kd) mice, suggesting that ezrin is involved in their expression in the BBM.