spacer gif spacer gif spacer gif spacer gif spacer gif
QUICK SEARCH:   [advanced]


spacer gif
     Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents    

First published online May 15, 2009
Journal of Experimental Biology 212, 1697-1706 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.028563
This Article
Right arrow Summary Freely available
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Related articles in JEB
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Google Scholar
Right arrow Articles by Boron, W. F.
Right arrow Articles by Parker, M. D.
PubMed
Right arrow Articles by Boron, W. F.
Right arrow Articles by Parker, M. D.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

Modular structure of sodium-coupled bicarbonate transporters

Walter F. Boron, Liming Chen and Mark D. Parker*

Department of Physiology and Biophysics, Case Western Reserve University Medical School, 10900 Euclid Avenue, Cleveland, OH 44106, USA


Figure 1
View larger version (13K):
[in this window]
[in a new window]

  		Fig. 1. Acid–base transporters. Acid–base homeostasis is achieved by the balanced action of acid-loading and acid-extruding mechanisms. (A) Acid loaders. The influx of acid equivalents across cell membranes is mediated by acid-loading transporters such as anion exchangers, electrogenic Na+-coupled bicarbonate transporters and HCO3 channels. (B) Acid extruders. The efflux of acid equivalents across cell membranes is mediated by acid-extruding transporters such as H-pumps, Na–H exchangers, and both electrogenic and electroneutral Na+-coupled bicarbonate transporters.

 

Figure 2
View larger version (9K):
[in this window]
[in a new window]

  		Fig. 2. Three-domain structure of a generic mammalian Na+-coupled HCO3 transporter (NCBT). By comparison with the predicted topology of the Cl–HCO3 exchanger AE1 (Askin et al., 1998Go; Fujinaga et al., 1999Go; Zhu et al., 2003Go), NCBTs are predicted to have an extended N-terminus (Nt), a transmembrane domain including 12–14 transmembrane spans (TMD), and a shorter C-terminal domain (Ct). An extended extracellular loop connecting transmembrane spans 5 and 6 includes multiple N-glycosylation sites.

 

Figure 3
View larger version (6K):
[in this window]
[in a new window]

  		Fig. 3. Net transport activity of mammalian NCBTs. NBCe1 and NBCe2 are both electrogenic NCBTs capable of mediating Na+:2 HCO3– influx or Na+:3 HCO3– efflux in a tissue-specific manner. NBCn1, NBCn2 and NDCBE are all electroneutral NCBTs that mediate net HCO3– influx. NBCn1 is associated with a Na+ conductance (dashed arrow). Na/HCO3 influx mediated by NDCBE is coupled to Cl– efflux.

 

Figure 4
View larger version (66K):
[in this window]
[in a new window]

  		Fig. 4. Alignment of protein modules comprising NCBT variants. NCBT variants are aligned to scale from Nt to Ct. Numbered gray columns mark the putative positions of the transmembrane helices represented in Fig. 2. Conservation of color in a vertical direction on the figure represents conservation of sequence among NCBTs. Internal splice cassettes are represented as green boxes and labeled with their name. PDZ-binding motifs (PDZ) and glycine-rich regions (Gly) are also marked. A horizontal line connecting bars represents the absence of homologous sequence in a variant. The position of conserved regions (CRs) and variable regions (VRs) discussed in the text are indicated by lines at the bottom of the diagram. Unless otherwise stated, protein sequences are human. Alignment is based on a manually adjusted version of a sequence alignment that was originally generated by ClustalW (http://www.ebi.ac.uk/Tools/clustalw2/index.html) using GenBank protein accession numbers for NBCe1-A (NP_003750), NBCe1-B (AAD42020), NBCe1-C (ABQ43327), NBCe2a (AAK26741), NBCe2c (AAK97072), NBCn1-A (Q9Y6M7), rat NBCn1-B (AAD46389), NBCn1-C (ACH61962), NBCn1-D (ACH61960), NBCn1-E (ACH61961), NBCn1-F (AAG16773), NBCn1-G (ACB47400), NBCn1-H (ACH61958), NBCn2-A (NP_071341), NBCn2-B (AAQ83632), rat NBCn2-C (AAS89263), rat NBCn2-D (derived in silico from rat NBCn2-C), NDCBE-A (AAY79176), NDCBE-B (NP_004849), NDCBE-C (ABJ09587) and NDCBE-D (ABJ91577).

 

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?



© The Company of Biologists Ltd 2009