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PDBsum entry 3r68
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Signaling protein
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PDB id
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3r68
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References listed in PDB file
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Key reference
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Title
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Identification of the pdz3 domain of the adaptor protein pdzk1 as a second, Physiologically functional binding site for the c terminus of the high density lipoprotein receptor scavenger receptor class b type i.
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Authors
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O.Kocher,
G.Birrane,
A.Yesilaltay,
S.Shechter,
R.Pal,
K.Daniels,
M.Krieger.
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Ref.
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J Biol Chem, 2011,
286,
25171-25186.
[DOI no: ]
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PubMed id
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Abstract
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The normal expression, cell surface localization, and function of the murine
high density lipoprotein receptor scavenger receptor class B type I (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 (Tyr(20) → Ala) only partially, rather than
completely, suppresses the ability of PDZK1 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 (K(d) = 37.0 μm), albeit with ∼10-fold lower
affinity than PDZ1. This binding is abrogated by a Tyr(253) → Ala
substitution. Comparison of the 1.5-Å resolution crystal structure of PDZ3
with its bound target peptide ((505)QEAKL(509)) to that of peptide-bound PDZ1
indicated fewer target peptide stabilizing atomic interactions (hydrogen bonds
and hydrophobic interactions) in PDZ3. A double (Tyr(20) → Ala (PDZ1) +
Tyr(253) → Ala (PDZ3)) substitution abrogated all target peptide binding to
PDZK1. In vivo hepatic expression of a singly substituted (Tyr(253) → Ala
(PDZ3)) PDZK1 transgene (Tg) was able to correct all of the SR-BI-related
defects in PDZK1 knock-out mice, whereas the doubly substituted [Tyr(20) → Ala
(PDZ1) + Tyr(253) → Ala (PDZ3)]Tg was unable to correct these defects. Thus,
we conclude that PDZK1-mediated control of hepatic SR-BI requires direct binding
of the SR-BI C terminus to either the PDZ1 or PDZ3 domains, and that binding to
both domains simultaneously is not required for PDZK1 control of hepatic SR-BI.
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