HMM Summary Page: TIGR00817

FunctionTpt phosphate/phosphoenolpyruvate translocator
Gene Symboltpt
Trusted Cutoff317.90
Domain Trusted Cutoff317.90
Noise Cutoff210.60
Domain Noise Cutoff210.60
Isology Typesubfamily
HMM Length302
Mainrole CategoryHypothetical proteins
Subrole CategoryConserved
AuthorPaulsen IT, Saier MH, Loftus BJ
Entry DateJul 7 2000 1:41PM
Last ModifiedFeb 14 2011 3:27PM
CommentThe 6-8 TMS Triose-phosphate Transporter (TPT) Family (TC 2.A.7.9) Functionally characterized members of the TPT family are derived from the inner envelope membranes of chloroplasts and nongreen plastids of plants. However, homologues are also present in yeast. Saccharomyces cerevisiae has three functionally uncharacterized TPT paralogues encoded within its genome. Under normal physiological conditions, chloroplast TPTs mediate a strict antiport of substrates, frequently exchanging an organic three carbon compound phosphate ester for inorganic phosphate (Pi). Normally, a triose-phosphate, 3-phosphoglycerate, or another phosphorylated C3 compound made in the chloroplast during photosynthesis, exits the organelle into the cytoplasm of the plant cell in exchange for Pi. However, experiments with reconstituted translocator in artificial membranes indicate that transport can also occur by a channel-like uniport mechanism with up to 10-fold higher transport rates. Channel opening may be induced by a membrane potential of large magnitude and/or by high substrate concentrations. Nongreen plastid and chloroplast carriers, such as those from maize endosperm and root membranes, mediate transport of C3 compounds phosphorylated at carbon atom 2, particularly phosphenolpyruvate, in exchange for Pi. These are the phosphoenolpyruvate:Pi antiporters (PPT). Glucose-6-P has also been shown to be a substrate of some plastid translocators (GPT). The three types of proteins (TPT, PPT and GPT) are divergent in sequence as well as substrate specificity, but their substrate specificities overlap.
ReferencesA2 hmmalign SE Ipaulsen AL clustalw_manual