Modular organization of the PDZ domains in the human discs-large protein suggests a mechanism for coupling PDZ domain-binding proteins to ATP and the membrane cytoskeleton.

Abstract	The human homologue (hDIg) of the Drosophila discs-large tumor suppressor (DIg) is a multidomain protein consisting of a carboxyl-terminal guanylate kinase-like domain, an SH3 domain, and three slightly divergent copies of the PDZ (DHR/GLGF) domain. Here have examined the structural organization of the three PDZ domains of hDIg using a combination of protease digestion and in vitro binding measurements. Our results show that the PDZ domains are organized into two conformationally stable modules one (PDZ, consisting of PDZ domains 1 and 2, and the other (PDZ) corresponding to the third PDZ domain. Using amino acid sequencing and mass spectrometry, we determined the boundaries of the PDZ domains after digestion with endoproteinase Asp-N, trypsin, and alpha-chymotrypsin. The purified PDZ1+2, but not the PDZ3 domain, contains a high affinity binding site for the cytoplasmic domain of Shaker-type K+ channels. Similarly, we demonstrate that the PDZ1+2 domain can also specifically bind to ATP. Furthermore, we provide evidence for an in vivo interaction between hDIg and protein 4.1 and show that the hDIg protein contains a single high affinity protein 4.1-binding site that is not located within the PDZ domains. The results suggest a mechanism by which PDZ domain-binding proteins may be coupled to ATP and the membrane cytoskeleton via hDlg.
Authors	S M Marfatia, J H Morais Cabral, L Lin, C Hough, P J Bryant, L Stolz, A H Chishti
Journal	The Journal of cell biology (J Cell Biol) Vol. 135 Issue 3 Pg. 753-66 (Nov 1996) ISSN: 0021-9525 [Print] United States
PMID	8909548 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
Chemical References	Cytoskeletal Proteins Drosophila Proteins Insect Hormones KCNA4 protein, human Kv1.4 Potassium Channel Membrane Proteins Neuropeptides Phosphoproteins Potassium Channels Potassium Channels, Voltage-Gated Recombinant Fusion Proteins Tumor Suppressor Proteins erythrocyte membrane band 4.1 protein erythrocyte membrane protein band 4.1-like 1 ezrin dlg1 protein, Drosophila Adenosine Triphosphate Endopeptidases
Topics	Adenosine Triphosphate (metabolism) Amino Acid Sequence Binding Sites Cytoskeletal Proteins Cytoskeleton Drosophila Proteins Elliptocytosis, Hereditary (blood) Endopeptidases Erythrocyte Membrane (chemistry) Humans Insect Hormones (blood, chemistry, metabolism) Kinetics Kv1.4 Potassium Channel Membrane Proteins (blood) Molecular Sequence Data Molecular Weight Neuropeptides Phosphoproteins (blood, metabolism) Potassium Channels (metabolism) Potassium Channels, Voltage-Gated Protein Binding Protein Structure, Tertiary Recombinant Fusion Proteins (chemistry, metabolism) Sequence Alignment Tumor Suppressor Proteins

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