Analysis of the human guanylin gene and the processing and cellular localization of the peptide

The complete cell biological analysis of human guanylin, a recently discovered regulatory peptide, is offered in this investigation: (i) the nucleotide sequence of the gene, (ii) the isolation and characterization of its circulating molecular form, and (iii) its localization in enterochromaffin cells of the gut. As determined by molecular cloning, DNA sequencing, and comparison with the known cDNA sequence, the approximately 2.6-kbp large gene consists of three exons interrupted by two introns. The putative promoter region contains a TTTAAAA sequence motif and several potential binding sites for transcription factors such as AP-1, AP-2, Sp 1, and glucocorticoid receptors. The isolated hormonal form of guanylin is a 94-amino acid peptide with a molecular mass of 10.3 kDa. Western blot analysis of RP-HPLC fractions from blood plasma confirms this molecular form. Thus, guanylin is synthesized by gut enterochromaffin cells as a prohormone of 115 amino acids and is processed to the molecular form of 94 amino acids circulating in the blood.