Prokaryote Transmembrane Transport


Transport Capabilities of Eleven Gram-positive Bacteria:
Comparative Genomic Analyses (PubMed) 
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2592090/?tool=pubmed   
Full length article online. 
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Membrane transport systems catalyze the uptake of essential nutrients, ions and metabolites, as well as the expulsion of toxic compounds, cell envelope macromolecules, secondary metabolites and the end products of metabolism. Transporters also participate in energy generation and interconversion, and they allow communication between cells and their environments. Transport is therefore essential to virtually every aspect of life.

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Five distinct well-defined types of functionally characterized transport systems, based upon mode of transport and energy coupling mechanism, are recognized by the TC (Transporter Classification) system [6, 7, 11]. These classes are: 

(1) channels,
(2) secondary carriers,
(3) primary active transporters,
(4) group translocators of the sugar transporting phosphoenolpyruvate-dependent phosphotransferase system, and
(5) transmembrane electron flow carriers.


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As summarized in Table 5, ABC transporters occur in substantial numbers in all Gram-positive bacteria studied."  My comment: if you click on the link, you'll see that there're more than just a few of them. 

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The fully sequenced genomes of eleven Gram-positive bacteria were searched for homologues in TCDB (probably 'Transporter Classification Data Base') in order to analyze the transport capabilities of these bacteria. These eleven bacteria devote at least 13 to 18% of their genes to transport. Of the total known transport proteins encoded in these genomes, on average, about 48% constitute uptake systems, 32% constitute efflux systems, and 5% of the proteins encode systems that transport substrates bidirectionally (Table 6).
 

Connexins, pannexins, innexins: novel roles of “hemi-channels” (PubMed)   
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2656403/?tool=pubmed 
Full length article online. 
"The advent of multicellular organisms, some 800 million years ago, necessitated the development of  mechanisms for cell-to-cell synchronization ..." 
"... specific channels that in all animal classes are made by tetra-span integral membrane proteins ..." 

Click on: 
(Fig. 2)

"gap junctions ... the physical substrate of cell-to-cell communication ..."  "the connexons of one cell align with, and strongly bind to the connexons of an adjacent cell, establishing a continuous intercellular hydrophilic pathway 
for the cell-to-cell exchange of multiple types of cytosolic molecules ..." 

Click on: 
(Fig. 1)

"... some of these proteins may also form  functional channels in domains of the cell membrane that are not involved in cell contact. ... these channels were found to allow for the leakage of cytosolic molecules, notably ATP and glutamate, into the extracellular medium and to permit the reverse uptake into cells ..." 

 





 







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