protein complex in the brush-border membrane explains a Hartnup disorder allele

• Published in: The FASEB journal 2008-08, Vol.22 (8), p.2880-2887
• Main Authors: Kowalczuk, Sonja, Bröer, Angelika, Tietze, Nadine, Vanslambrouck, Jessica M, Rasko, John E.J, Bröer, Stefan
• Format: Article
• Language: English
• Subjects: Alleles; Amino Acid Substitution; amino acid transport; Amino Acid Transport Systems, Neutral - chemistry; Amino Acid Transport Systems, Neutral - genetics; Amino Acid Transport Systems, Neutral - metabolism; angiotensin-converting enzyme 2; Animals; Base Sequence; DNA Primers - genetics; epithelial transport; Female; Hartnup Disease - genetics; Hartnup Disease - metabolism; Humans; In Vitro Techniques; Intestine, Small - metabolism; Kidney - metabolism; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Mice; Microvilli - metabolism; Models, Molecular; Multiprotein Complexes; Mutation; Oocytes - metabolism; Peptidyl-Dipeptidase A - chemistry; Peptidyl-Dipeptidase A - genetics; Peptidyl-Dipeptidase A - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Xenopus laevis
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fj.08-107300

Protein absorption in the intestine is mediated by proteases and brush-border peptidases together with peptide and amino acid transporters. Neutral amino acids are generated by a variety of aminopeptidases and carboxypeptidases and are subsequently taken up by the amino acid transporter B⁰AT1 (SLC6A19), which is mutated in Hartnup disorder. Coexpression of B⁰AT1 together with the brush-border carboxypeptidase angiotensin-converting enzyme 2 (ACE2) in Xenopus laevis oocytes led to a dramatic increase of transporter expression at the oocyte surface. Other members of the SLC6 family were not stimulated by coexpression with ACE2. Addition of a peptide containing a carboxyterminal leucine residue to ACE2- and B⁰AT1-coexpressing oocytes caused inward currents due to Na⁺-leucine cotransport, demonstrating the formation of a metabolic complex. Coexpression of the Hartnup disorder causing mutation B⁰AT1(R240Q) showed reduced interaction with ACE2 and its renal paralogue collectrin. This would result in reduced surface expression in both kidney and intestine, thereby explaining the onset of the disorder in individuals carrying this mutation.--Kowalczuk, S., Bröer, A., Tietze, N., Vanslambrouck, J. M., Rasko, J. E. J., Bröer, S. A protein complex in the brush-border membrane explains a Hartnup disorder allele.