3r68

Publication Abstract from PubMed

The normal expression, cell surface localization and function of the murine HDL receptor SR-BI in hepatocytes in vivo - and thus normal lipoprotein metabolism - depend on its four PDZ domain (PDZ1-PDZ4) containing cytoplasmic adaptor protein PDZK1. Previous studies showed that the C-terminus of SR-BI (target peptide) binds directly to PDZ1 and influences hepatic SR-BI protein expression. Unexpectedly an inactivating mutation in PDZ1 (20Tyr-->Ala) only partially, rather than completely, suppresses PDZK1's ability to control hepatic SR-BI. We used isothermal titration calorimetry to show that PDZ3, but not PDZ2 or PDZ4, can also bind the target peptide (Kd= 37.0 muM), albeit with ~10-fold lower affinity than PDZ1. This binding is abrogated by a 253Tyr-->Ala substitution. Comparison of the 1.5 A resolution crystal structure of PDZ3 with its bound target peptide (505QEAKL509) to that of peptide-bound PDZ1 indicated fewer target peptide stabilizing atomic interactions (hydrogen bonds and hydrophobic interactions) in PDZ3. A double [20Tyr-->Ala (PDZ1) + 253Tyr-->Ala (PDZ3)] substitution abrogated all target peptide binding to PDZK1. In vivo hepatic expression of a singly substituted (253Tyr-->Ala (PDZ3)) PDZK1 transgene (Tg) was able to correct all of the SR-BI-related defects in PDZK1 KO mice, whereas the doubly substituted [20Tyr-->Ala (PDZ1) + 253Tyr-->Ala (PDZ3)]-Tg was unable to correct these defects. Thus, we conclude that PDZK1-mediated control of hepatic SR-BI requires direct binding of SR-BI's C-terminus to either the PDZ1 or PDZ3 domain, and that binding to both domains simultaneously is not required for PDZK1 control of hepatic SR-BI.

Identification of the PDZ3 domain of the adaptor protein PDZK1 as a second, physiologically functional, binding site for the C-terminus of the HDL receptor SR-BI.,Kocher O, Birrane G, Yesilaltay A, Shechter S, Pal R, Daniels K, Krieger M J Biol Chem. 2011 May 23. PMID:21602281^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.