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C C Fritz

Publications and source records attributed to C C Fritz.

8 recordsLinked to original sources
PubMed2001

Solution structure of B. subtilis acyl carrier protein.

BACKGROUND: Acyl carrier protein (ACP) is a fundamental component of fatty acid biosynthesis in which the fatty acid chain is elongated by the fatty acid synthetase system while attached to the 4'-phosphopantetheine prosthetic group (4'-PP) of ACP. Activation of ACP is mediated by holo-acyl carrier protein synthase (ACPS) when ACPS transfers the 4'-PP moiety from coenzyme A (CoA) to Ser36 of apo-ACP. Both ACP and ACPS have been identified as essential for E. coli viability and potential targets for development of antibiotics. RESULTS: The solution structure of B. subtilis ACP (9 kDa) has been determined using two-dimensional and three-dimensional heteronuclear NMR spectroscopy. A total of 22 structures were calculated by means of hybrid distance geometry-simulated annealing using a total of 1,050 experimental NMR restraints. The atomic rmsd about the mean coordinate positions for the 22 structures is 0.45 +/- 0.08 A for the backbone atoms and 0.93 +/- 0.07 A for all atoms. The overall ACP structure consists of a four alpha-helical bundle in which 4'-PP is attached to the conserved Ser36 that is located in alpha helix II. CONCLUSIONS: Structural data were collected for both the apo and holo forms of ACP that suggest that the two forms of ACP are essentially identical. Comparison of the published structures for E. coli ACP and actinorhodin polyketide synthase acyl carrier protein (act apo-ACP) from Streptomyces coelicolor A3(2) with B. subtilis ACP indicates similar secondary structure elements but an extremely large rmsd between the three ACP structures (>4.3 A). The structural difference between B. subtilis ACP and both E. coli and act apo-ACP is not attributed to an inherent difference in the proteins, but is probably a result of a limitation in the methodology available for the analysis for E. coli and act apo-ACP. Comparison of the structure of free ACP with the bound form of ACP in the ACP-ACPS complex reveals a displacement of helix II in the vicinity of Ser36. The induced perturbation of ACP by ACPS positions Ser36 proximal to coenzyme A and aligns the dipole of helix II to initiate transfer of 4'-PP to ACP.

Acyl Carrier Protein↗
PubMed2000

Crystal structures of substrate binding to Bacillus subtilis holo-(acyl carrier protein) synthase reveal a novel trimeric arrangement of molecules resulting in three active sites.

BACKGROUND: Holo-(acyl carrier protein) synthase (AcpS), a member of the phosphopantetheinyl transferase superfamily, plays a crucial role in the functional activation of acyl carrier protein (ACP) in the fatty acid biosynthesis pathway. AcpS catalyzes the attachment of the 4'-phosphopantetheinyl moiety of coenzyme A (CoA) to the sidechain of a conserved serine residue on apo-ACP. RESULTS: We describe here the first crystal structure of a type II ACP from Bacillus subtilis in complex with its activator AcpS at 2.3 A. We also have determined the structures of AcpS alone (at 1.8 A) and AcpS in complex with CoA (at 1.5 A). These structures reveal that AcpS exists as a trimer. A catalytic center is located at each of the solvent-exposed interfaces between AcpS molecules. Site-directed mutagenesis studies confirm the importance of trimer formation in AcpS activity. CONCLUSIONS: The active site in AcpS is only formed when two AcpS molecules dimerize. The addition of a third molecule allows for the formation of two additional active sites and also permits a large hydrophobic surface from each molecule of AcpS to be buried in the trimer. The mutations Ile5-->Arg, Gln113-->Glu and Gln113-->Arg show that AcpS is inactive when unable to form a trimer. The co-crystal structures of AcpS-CoA and AcpS-ACP allow us to propose a catalytic mechanism for this class of 4'-phosphopantetheinyl transferases.

Acyl Carrier Protein↗
PubMed1996

HIV Rev uses a conserved cellular protein export pathway for the nucleocytoplasmic transport of viral RNAs.

BACKGROUND: The structural proteins of human immunodeficiency virus type 1 (HIV-1) are encoded by intron-containing mRNAs that normally are retained in the nucleus. A viral regulatory protein, Rev, specifically induces the accumulation of these transcripts in the cytoplasm. Rev is an RNA-binding protein that also contains an 'effector' domain. The Rev effector domain has recently been shown to function as an autonomous nuclear export signal (NES) that, when fused to a foreign protein, will cause its rapid nuclear export. We and others have recently reported the cloning of a human protein (hRIP/Rab), that specifically interacts with the effector domain of Rev. RESULTS: Here we show that the NESs contained within two cellular proteins, PKI and I kappa B, which are not involved in RNA metabolism, also interact with hRIP. Fusion of these cellular sequences to the Rev RNA-binding domain reconstitutes a functional Rev protein. In addition to hRIP, these NESs also bind to several nuclear pore complex (NPC). We show that this protein export pathway is highly conserved by demonstrating that mammalian NESs also function in yeast. CONCLUSIONS: Our results indicate that the HIV-1 Rev protein evolved to take advantage of a cellular protein export pathway in order to allow the nucleocytoplasmic transport of unspliced viral RNA. Our data suggest a model in which the export substrate is translocated through the NPC by sequential interactions with different nucleoporins. Finally, our experiment suggests a mechanism by which I kappa B can downregulate nuclear NF kappa B activity by causing its rapid export from the nucleus.

Binding Sites↗
PubMed1995

A human nucleoporin-like protein that specifically interacts with HIV Rev.

The Rev protein of human immunodeficiency virus type 1 (HIV-1) facilitates the nuclear export of unspliced and partly spliced viral RNAs. Rev contains an RNA binding domain, required for interaction with HIV-1 RNA, and an effector domain, required for RNA-bound Rev to function. The Rev effector domain is believed to interact with a cellular cofactor required for the Rev response and thus HIV-1 replication. Here we report the use of a yeast two-hybrid screen to clone human Rev interacting protein (hRIP), which specifically interacts with the Rev effector domain. This hRIP protein has homology with nucleoporins, a class of proteins that mediate nucleocytoplasmic transport. These and other properties of hRIP are those expected of a Rev cellular cofactor.

Amino Acid Sequence↗
PubMed1993

The gene family encoding the ribulose-(1,5)-bisphosphate carboxylase/oxygenase (Rubisco) small subunit of potato.

We determined the nucleotide sequences of five members of the rbcS gene family encoding the small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of potato. The genomic organization, structure and expression of the genes is compared to the features of the rbcS genes in tomato. Within the two species, Lycopersicon esculentum and Solanum tuberosum, both members of the Solanaceae, the rbcS genes share more interspecific sequence identity, especially in the 5'- and 3'-untranslated regions and the intron sequences, than within one species. However, the expression data of orthologous rbcS genes containing highly identical regulatory cis-acting elements were found to be different, suggesting that the simple finding of these motifs does not automatically imply similar transcriptional and/or post-transcriptional gene regulation.

Amino Acid Sequence↗
PubMed1991

Reduced steady-state levels of rbcS mRNA in plants kept in the dark are due to differential degradation.

When plants are placed in the dark, the level of the abundant mRNA encoding the small subunit of ribulose-1,5-bisphosphate carboxylase (rbcS) declines rapidly. We present evidence demonstrating an active degradation of rbcS mRNA in the dark. Detailed analysis shows that transcripts originating from different members of the rbcS gene family are differentially affected by this degradation. This phenomenon is not common to all light-regulated plant genes since the mRNA for ST-LS1, another leaf-specific and light-induced gene, is not degraded in the dark within the same time scale.

Base Sequence↗
PubMed1988

rbcS genes in Solanum tuberosum: conservation of transit peptide and exon shuffling during evolution.

Five genes of the rbcS gene family of Solanum tuberosum (potato) were studied. One of these is a cDNA clone; the other four are located on two genomic clones representing two different chromosomal loci containing one (locus 1) and three genes (locus 2), respectively. The intron/exon structure of the three genes in locus 2 is highly conserved with respect to size and position. These genes contain two introns, whereas the gene from locus 1 contains three introns. Although in most cases the amino acid sequences in the transit peptide part of different rbcS genes from the same species varied considerably more than the corresponding mature amino acid sequences, one exception found in tomato and potato indicates that the transit peptide of rbcS could have a special function. A comparison of the rbcS genes of higher plants with those of prokaryotes offers suggestive evidence that introns first served as spacer material in the process of exon shuffling and then were removed stepwise during the evolution of higher plants.

Amino Acid Sequence↗