Proline transport protein

The proline transport protein prnB of Aspergillus nidulans [47] is very similar to the above-mentioned family of Saccharomyces cerevisiae amino acid transporters (about 42% identity with the PUT4 gene product and 30% identity with the CANl and the HIP I gene products). So is the AroP general aromatic amino acid transporter protein of Escherichia coli K-12, which has about 30% identity with the HIPI gene product [48]. Both hydrophilic ends are very different from one transporter to another (see Fig. 2). 

The Na+/proline transporter of E. coli (PutP) is an integral membrane protein that is proposed to contain 13 transmembrane helices.85 Four-pulse DEER measurements found distances of 48,22, and 18 A for three doubly spin-labelled variants.The 48 A distance confirmed that those two labels were on opposite sides of the membrane. The large distance distribution widths that were observed in the pair functions reveal the substantial flexibility of the loop regions to which the spin labels were attached. 

On the basis of this limited evidence, the most feasible conclusion is that hydroxy-L-proline-rich protein, synthesized on ribosomes, is glycosylated in the Golgi bodies, transported to the cell surface in Golgi vesi-... 

Haardt, M., Kempf, B., Faatz, E. and Bremer, E. (1995). The osmoprotectant proline betaine is a major substrate for the binding-protein-dependent transport system ProU of Escherichia coli K-12, Mol. Gen. Genet., 246, 783-786. 

The successful use of [ F]FDG in oncology PET imaging has prompted the design of several other radiopharmaceuticals, such as [ F]FLT ([ F]fluorothymi-dine, used as cellular proliferation marker. Scheme 36) [152-154], F-MISO ([ F] fluoromisonidazole, used to assess tissue hypoxia. Scheme 37) [155], c/s-4-[ F] fluoro-L-proline (used as abnormal collagen synthesis marker. Scheme 38) [156] and 0-(2-[ F]fluoroethyl)-L-tyrosine (used as amino acid transport and/or protein synthesis marker. Scheme 39) [157]. All these fluorine-18-labelled molecules have been prepared by aliphatic nucleophilic fluorination followed by a deprotection reaction. 

Many natural channels, particularly those for simple ions, form at the confluence of complex proteins. This mechanism has been simplified by the Gokel group which has prepared alkyl-terminated hexapeptides that contain a short proline containing peptide sequence, GGGPGGG, similar to that found in natural Cl -selective channels [14], These compounds give Cl- selectivity when anchored in phospholipid vesicles. It is assumed that channels form by supramolecular aggregation of the hexapeptides around the proline motif, shown in Fig. 5.6. Such a simple transport mechanism has yet to be seen in Nature but it would not be too surprising if one were to be found. 

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