Figure 2.

Mucins form a charge selective permeability barrier to peptides. (a) A suite of peptides of equal molecular weight but with different net charge and spatial charge distributions are used as probes to test mucin barrier permeability. Note the block and alternate peptides are molecular isomers. (b) Time series of fluorescence peptides entering a 0.5% (w/v) mucin barrier at 20 mM NaCl ionic strength show different transport behaviors of the cationic and anionic peptides. (c) Fluorescence images are analyzed across the midline of the microfluidic mucin channel (marked by dotted arrow labeled x in Fig. 2b) to obtain peptide concentration profiles in the absence and presence of 0.5% (w/v) mucins. The peptide profiles of the two peptides differ in the presence of mucins but are shaped identically when mucins are absent, demonstrating that mucins are responsible for the selective transport of the peptides.