Title : N-Glycosylation dictates proper processing of organic anion transporting
polypeptide 1B1
Abstract :
- Organic anion transporting polypeptides ( OATPs ) have been extensively recognized as key determinants of absorption, distribution, metabolism and excretion (ADME) of various drugs, xenobiotics and toxins
- Putative N-glycosylation sites located in the extracellular loops 2 and 5 is considered a common feature of all OATPs and some members have been demonstrated to be glycosylated proteins
- However, experimental evidence is still lacking on how such a post-translational modification affect the transport activity of OATPs and which of the putative glycosylation sites are utilized in these transporter proteins
- In the present study, we substituted asparagine residues that are possibly involved in N-glycosylation with glutamine residues and identified three glycosylation sites ( Asn134, Asn503 and Asn516 ) within the structure of OATP1B1 , an OATP member that is mainly expressed in the human liver
- Our results showed that Asn134 and Asn516 are used for glycosylation under normal conditions; however, when Asn134 was mutagenized, an additional asparagine at position 503 is involved in the glycosylation process
- Simultaneously replacement of all three asparagines asparagines with glutamines led to significantly reduced protein level as well as loss of transport activity
- Further studies revealed that glycosylation affected stability of the transporter protein and the unglycosylated mutant was retained within endoplasmic reticulum