Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.26 (invertase)
 4,927 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ypt1p of Saccharomyces cerevisiae is a ras-related GTP-binding protein that fulfils an essential function in intracellular protein transport between the endoplasmic reticulum (ER) and the Golgi complex. Ypt proteins from yeasts and mammals that share an identical sequence in the region analogous to the ras effector domain are functionally interchangeable. We analyzed the function of the putative effector domain of yeast Ypt1p (amino acids 37-45) using site-directed mutagenesis and gene replacement. Four out of six point mutations leading to single amino acid substitutions (Y37F, S39A, T40S and V43E) did not cause any particular phenotype. ypt1(I41M) mutants were inviable whereas ypt1(D44N) mutant cells were temperature sensitive at 37 degrees C and accumulated core-glycosylated invertase at the nonpermissive temperature. This mutant also accumulated ER and small vesicles both at 25 degrees C and 37 degrees C. From porcine liver we identified and partially purified a GTPase-activating protein (yptGAP) that is similarly active with mouse ypt1p/rab1p and yeast Ypt1p but is inactive with H-ras protein as a substrate. Although none of the yeast ypt1 mutant proteins were significantly impaired in their ability to bind GTP, purified ypt1(D44N)p responded only partially and ypt1(I41M)p did not respond at all, to yptGAP. Thus we suggest that analogous to rasGAP/H-ras p21 interaction in mammalian cells, yptGAP is an intracellular target of Ypt1p, interacting with the effector domain and regulating its GTPase activity, and that this interaction is required for the functioning of yeast Ypt1p in intracellular protein transport.
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PMID:Mutational analysis of the putative effector domain of the GTP-binding Ypt1 protein in yeast suggests specific regulation by a novel GAP activity. 200 58

The genes SEC4 and YPT1 encode Ras-related GTP-binding proteins in the yeast Saccharomyces cerevisiae. Ypt1 is necessary for vesicular transport from the endoplasmic reticulum to the Golgi, whereas Sec4 is required for fusion of post-Golgi secretory vesicles to the plasma membrane. Recently, three structural domains have been proposed to specify the stage in cellular transport at which members of the Sec4/Ypt1/Rab family act: the effector domain, the C-terminal hypervariable region, and a region corresponding to loop 7 in the structure of p21ras (ref. 8). Here we use Sec4/Ypt1 chimaeras to show that these three regions cooperate to specify Ypt1 function and that the C-terminal hypervariable region is needed for Ypt1 localization to the Golgi. Unexpectedly, we found that a single chimaera can function as either Ypt1 or Sec4 without missorting carboxypeptidase Y or invertase.
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PMID:Interactions of three domains distinguishing the Ras-related GTP-binding proteins Ypt1 and Sec4. 846 98