Sensing of dietary protein is more complex as it is dependent on both peptide transporter 1 (PEPT1) which is a proton-dependent transporter of amino acids, di- and oligo-peptides, and the Ca2+ sensor Case, a class C GPCR that also recognises di- and oligo-peptides.
CasR is expressed both on enteroendorine cells, where it stimulates CCK and GLP-1 secretion, and on enterocytes, where it stimulates absorption of nutrients and stabilises intestinal barrier function.