Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Unlike most other organisms, the essential five-step coenzyme A biosynthetic pathway has not been fully resolved in yeast. Specifically, the genes encoding the phosphopantothenoylcysteine decarboxylase (PPCDC) activity still remain unidentified. Sequence homology analyses suggest three candidates-Ykl088w, Hal3 and Vhs3-as putative PPCDC enzymes in Saccharomyces cerevisiae. Notably, Hal3 and Vhs3 have been characterized as negative regulatory subunits of the Ppz1 protein phosphatase. Here we show that YKL088w does not encode a third Ppz1 regulatory subunit, and that the essential roles of Ykl088w and the Hal3 and Vhs3 pair are complementary, cannot be interchanged and can be attributed to PPCDC-related functions. We demonstrate that while known eukaryotic PPCDCs are homotrimers, the active yeast enzyme is a heterotrimer that consists of Ykl088w and Hal3/Vhs3 monomers that separately provides two essential catalytic residues. Our results unveil Hal3 and Vhs3 as moonlighting proteins involved in both CoA biosynthesis and protein phosphatase regulation.
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PMID:Moonlighting proteins Hal3 and Vhs3 form a heteromeric PPCDC with Ykl088w in yeast CoA biosynthesis. 1991 31

The Saccharomyces cerevisiae Hal3 protein is a moonlighting protein, able to function both as an inhibitory subunit of the Ppz1 protein phosphatase and as a constituent protomer of an unprecedented heterotrimeric PPCDC (phosphopantothenoylcysteine decarboxylase), the third enzyme of the CoA biosynthetic pathway. In the present study we initiated the dissection of the structural elements required for both disparate cellular tasks by using a combination of biochemical and genetic approaches. We show that the conserved Hal3 core [PD (PPCDC domain)] is necessary for both functions, as determined by in vitro and in vivo assays. The Hal3 NtD (N-terminal domain) is not functional by itself, although in vitro experiments indicate that when this domain is combined with the core it has a relevant function in Hal3's heteromeric PPCDC activity. Both the NtD and the acidic CtD (C-terminal domain) also appear to be important for Hal3's Ppz1 regulatory function, although our results indicate that the CtD fulfils the key role in this regard. Finally, we show that the introduction of two key asparagine and cysteine residues, essential for monofunctional PPCDC activity but absent in Hal3, is not sufficient to convert it into such a homomeric PPCDC, and that additional modifications of Hal3's PD aimed at increasing its resemblance to known PPCDCs also fails to introduce this activity. This suggests that Hal3 has undergone significant evolutionary drift from ancestral PPCDC proteins. Taken together, our work highlights specific structural determinants that could be exploited for full understanding of Hal3's cellular functions.
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PMID:Functional mapping of the disparate activities of the yeast moonlighting protein Hal3. 2212 81

Saccharomyces cerevisiae Hal3 and Vhs3 are moonlighting proteins, acting both as inhibitors of the serine/threonine protein phosphatase Ppz1 and as subunits (together with Cab3) of the unique heterotrimeric phosphopantothenoylcysteine decarboxylase (PPCDC) enzyme of Hemiascomycetous yeast. Both these roles are essential: PPCDC catalyses the third step of coenzyme A biosynthesis, while Ppz1 inhibition is required for regulation of monovalent cation homeostasis. However, the mechanisms by which these proteins' disparate activities are regulated are not well understood. The PPCDC domains (PDs) of Hal3, Vhs3 and Cab3 constitute the minimum requirement for these proteins to show both PPCDC activity and, in the case of Hal3 and Vhs3, to bind to Ppz1. Using these PD proteins as a model system to study the possibility of dynamic interchange between these roles, we provide evidence that Hal3 binds Ppz1 as a monomer (1:1 stoichiometry), requiring it to de-oligomerize from its usual homo- and heterotrimeric states (the latter having PPCDC activity). This de-oligomerization is made possible by structural features that set Hal3 apart from Vhs3, increasing its ability to undergo monomer exchange. These findings suggest that oligomer interchange may be a significant factor in the functional regulation of these proteins and their various unrelated (moonlighting) functions.
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PMID:Complex stability and dynamic subunit interchange modulates the disparate activities of the yeast moonlighting proteins Hal3 and Vhs3. 2651 74

S. cerevisiae Hal3 (ScHal3) is a moonlighting protein that, is in its monomeric state, regulates the Ser/Thr protein phosphatase Ppz1, but also joins ScCab3 (and in some instances the Hal3 paralog Vhs3) to form an unusual heterotrimeric phosphopantothenoylcysteine decarboxylase (PPCDC) enzyme. PPCDC is required for CoA biosynthesis and in most eukaryotes is a homotrimeric complex with three identical catalytic sites at the trimer interfaces. However, in S. cerevisiae the heterotrimeric arrangement results in a single functional catalytic center. Importantly, the specific structural determinants that direct Hal3's oligomeric state and those required for Ppz1 inhibition remain largely unknown. We mutagenized residues in the predicted hydrophobic core of ScHal3 (L403-L405) and the plant Arabidopsis thaliana Hal3 (AtHal3, G115-L117) oligomers and characterized their properties as PPCDC components and, for ScHal3, also as Ppz1 inhibitor. We found that in AtHal3 these changes do not affect trimerization or PPCDC function. Similarly, mutation of ScHal3 L403 has no effect. In contrast, ScHal3 L405E fails to form homotrimers, but retains the capacity to bind Cab3-explaining its ability to rescue a hal3 vhs3 synthetically lethal mutation. Remarkably, the L405E mutation decreases Hal3's ability to interact with and to inhibit Ppz1, confirming the importance of the oligomer/monomer equilibrium in Hal3's Ppz1 regulating function.
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PMID:Mutations at the hydrophobic core affect Hal3 trimer stability, reducing its Ppz1 inhibitory capacity but not its PPCDC moonlighting function. 3027 72