Updated FTP location. Cortical TECs from K5D1 and K5D1-β5tKO mice were lysed, reduced, alkylated, and subjected to methanol/chloroform precipitation. Proteins were digested with trypsin/Lys-C mix. The digests were desalted using GL-Tip SDB, and the eluates were evaporated in a SpeedVac concentrator and dissolved in 0.1% TFA. LC-MS/MS analysis of the resultant peptides (400 ng each) was performed on an EASY-nLC 1200 UHPLC connected to a Q Exactive Plus mass spectrometer. The mass spectrometer was operated in a data-dependent acquisition mode with a top 10 MS/MS method. MS1 spectra were measured with a resolution of 70,000, an AGC target of 1×106 and a mass range from 350 to 1,500 m/z. HCD MS/MS spectra were acquired at a resolution of 17,500, an AGC target of 5×104, an isolation window of 2.0 m/z, a maximum injection time of 60 msec and a normalized collision energy of 27. Dynamic exclusion was set to 10 sec. Raw data were directly analyzed against the Swiss-Prot database restricted to Mus musculus using Proteome Discoverer version 2.2 with Mascot search engine version 2.5 for identification and label-free precursor ion quantification. Peptides and proteins were filtered at a FDR of 1% using the percolator node and the protein FDR validator node, respectively. Normalization was performed such that the total sum of abundance values for each sample over all peptides was the same.