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First published online May 15, 2009
Journal of Experimental Biology 212, 1638-1646 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.028605

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NHE3 regulatory complexes

Mark Donowitz^*, Sachin Mohan, Cindy Xinjun Zhu, Tian-E Chen, Rong Lin, Boyoung Cha, Nicholas C. Zachos, Rakhilya Murtazina, Rafiquel Sarker and Xuhang Li

Johns Hopkins University School of Medicine, 720 Rutland Avenue Baltimore, MD 21205, USA

View larger version (9K): [in this window] [in a new window]   Fig. 1. Cartoon of mammalian small intestinal Na absorptive processes. Neutral NaCl absorption is made up of NHE3 linked to either DRA or PAT-1.

View larger version (79K): [in this window] [in a new window]   Fig. 2. (A) Model of the transport domain of NHE1 showing the area of exchange as two opposing funnel structures facing the intracellular and extracellular surfaces with membrane spanning domains indicated by roman numerals with critical amino acids shown. With permission from Landau et al. (Landau et al., 2007). (B) Comparison of NhaA and NHE1 transport domains, modeled from the crystal structure of NhaA. The homologus amino acids crucial to exchange of NhaA and NHE1 are shown. With permission from Landau et al. (Landau et al., 2007). (C) Amino acid alignment of human NHE1 (SLC9A1) and human NHE3 (SLC9A3) with arrows designating the amino acids shown in Fig. 2B, demonstrating identity. *, identical amino acids;:, conserved amino acids; ·, semi-conserved amino acids.

View larger version (4K): [in this window] [in a new window]   Fig. 3. Secondary structure prediction for human NHE3 C-terminus (amino acids 457–834) based on Chou-Fasman modeling (Chou and Fasman, 1974).

View larger version (30K): [in this window] [in a new window]   Fig. 4. Cartoon of domain structure of rabbit NHE3. The N-terminus includes amino acids 1–454. The C-terminus is the regulatory domain and in blue are some of the extracellular and second messenger regulators with the parts of the C-terminus necessary for their effects shown. In green is the area of attachment of NHE3 to the cytoskeleton via ezrin/radixin/moesin (ERM) proteins which associate with NHE3. In yellow are shown the proteins binding to and regulating the NHE3 C-terminus.

View larger version (37K): [in this window] [in a new window]   Fig. 5. (A) Sucrose density gradient centrifugation demonstrating NHE3 exists in multiple large complexes in all cells in which it is expressed. Lysates from the cells shown were Triton X-100 solubilized, separated by centrifugation and identified by immunoblotting with sizes shown in comparison with proteins of known size studied simultaneously on parallel gradients (E3HA, HA-NHE3). (B) Carbachol (Carb) exposure changed the NHE3 complex size. With permission from Li et al. (Li et al., 2004).

View larger version (44K): [in this window] [in a new window]   Fig. 6. Cartoon of `switch domain' of NHE3 which has been shown to dynamically associate with at least seven proteins in a short -helical domain (amino acids 586–605). We draw this as an interacting dimer although evidence that this is the organization structure of the C-terminus is lacking. Drawing by Virginia Ferrante (Ferrante Medical Media).

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