The combination of a candidate gene approach, column chromatography, and mass spectrometry identifies several fibroblast-derived proteins essential for endothelial cell sprouting and lumen formation. Furthermore, proteins responsible for EC lumen formation increase matrix stiffness, which correlates with EC lumenogenesis.

The class I terpenoid cyclase epi-isozizaene synthase (EIZS) utilizes the universal achiral isoprenoid substrate, farnesyl diphosphate, to generate epi-isozizaene as the predominant sesquiterpene cyclization product and at least five minor sesquiterpene products, making EIZS an ideal platform for the exploration of fidelity and promiscuity in a terpenoid cyclization reaction. The hydrophobic active site contour of EIZS serves as a template that enforces a single substrate conformation, and chaperones subsequently formed carbocation intermediates through a well-defined mechanistic sequence. Here, we have used the crystal structure of EIZS as a guide to systematically remold the hydrophobic active site contour in a library of 26 site-specific mutants. Remolded cyclization templates reprogram the reaction cascade not only by reproportioning products generated by the wild-type enzyme but also by generating completely new products of diverse structure. Specifically, we have tripled the overall number of characterized products generated by EIZS. Moreover, we have converted EIZS into six different sesquiterpene synthases: F96A EIZS is an (E)-β-farnesene synthase, F96W EIZS is a zizaene synthase, F95H EIZS is a β-curcumene synthase, F95M EIZS is a β-acoradiene synthase, F198L EIZS is a β-cedrene synthase, and F96V EIZS and W203F EIZS are (Z)-γ-bisabolene synthases. Active site aromatic residues appear to be hot spots for reprogramming the cyclization cascade by manipulating the stability and conformation of critical carbocation intermediates. A majority of mutant enzymes exhibit only relatively modest 2–100-fold losses of catalytic activity, suggesting that residues responsible for triggering substrate ionization readily tolerate mutations deeper in the active site cavity.

Fusicoccin A is a diterpene glucoside phytotoxin generated by the fungal pathogen Phomopsis amygdali that causes the plant disease constriction canker, first discovered in New Jersey peach orchards in the 1930’s. Fusicoccin A is also an emerging new lead in cancer chemotherapy. The hydrocarbon precursor of fusicoccin A is the tricyclic diterpene fusicoccadiene, which is generated by a bifunctional terpenoid synthase. Here, we report X-ray crystal structures of the individual catalytic domains of fusicoccadiene synthase: the C-terminal domain is a chain elongation enzyme that generates geranylgeranyl diphosphate, and the N-terminal domain catalyzes the cyclization of geranylgeranyl diphosphate to form fusicoccadiene. Crystal structures of each domain complexed with bisphosphonate substrate analogues suggest that three metal ions and three positively charged amino acid side chains trigger substrate ionization in each active site. While in vitro incubations reveal that the cyclase domain can utilize farnesyl diphosphate and geranyl diphosphate as surrogate substrates, these shorter isoprenoid diphosphates are mainly converted into acyclic alcohol or hydrocarbon products. Gel filtration chromatography and analytical ultracentrifugation experiments indicate that full-length fusicoccadiene synthase adopts hexameric quaternary structure, and small-angle X-ray scattering data yield a well-defined molecular envelope illustrating a plausible model for hexamer assembly.

Background: Aldehyde dehydrogenase isozymes ALDH1A1 and ALDH3A1 are highly expressed in non small cell lung cancer. Neither the mechanisms nor the biologic significance for such over expression have been studied.

A previously described mammalian cell activity, called VPg unlinkase, specifically cleaves a unique protein-RNA covalent linkage generated during the viral genomic RNA replication steps of a picornavirus infection. For over three decades, the identity of this cellular activity and its normal role in the uninfected cell had remained elusive. Here we report the purification and identification of VPg unlinkase as the DNA repair enzyme, 5′-tyrosyl-DNA phosphodiesterase-2 (TDP2). Our data show that VPg unlinkase activity in different mammalian cell lines correlates with their differential expression of TDP2. Furthermore, we show that recombinant TDP2 can cleave the protein-RNA linkage generated by different picornaviruses without impairing the integrity of viral RNA. Our results reveal a unique RNA repair-like function for TDP2 and suggest an unusual role in host-pathogen interactions for this cellular enzyme. On the basis of the identification of TDP2 as a potential antiviral target, our findings may lead to the development of universal therapeutics to treat the millions of individuals afflicted annually with diseases caused by picornaviruses, including myocarditis, aseptic meningitis, encephalitis, hepatitis, and the common cold.5′-tyrosyl-RNA phosphodiesterase | poliovirus | human rhinovirus | translation initiation

Due to the limited coding capacity of picornavirus genomic RNAs, host RNA binding proteins play essential roles during viral translation and RNA replication. Here we describe experiments suggesting that AUF1, a host RNA binding protein involved in mRNA decay, plays a role in the infectious cycle of picornaviruses such as poliovirus and human rhinovirus. We observed cleavage of AUF1 during poliovirus or human rhinovirus infection, as well as interaction of this protein with the 5′ noncoding regions of these viral genomes. Additionally, the picornavirus proteinase 3CD, encoded by poliovirus or human rhinovirus genomic RNAs, was shown to cleave all four isoforms of recombinant AUF1 at a specific N-terminal site in vitro. Finally, endogenous AUF1 was found to relocalize from the nucleus to the cytoplasm in poliovirus-infected HeLa cells to sites adjacent to (but distinct from) putative viral RNA replication complexes.

SUMMARY Two presumptive terpene synthases of unknown biochemical function encoded by the sscg_02150 and sscg_03688 genes of Streptomyces clavuligerus ATCC 27074 were individually expressed in Escherichia coli as N-terminal-His6-tag proteins, using codon-optimized synthetic genes. Incubation of recombinant SSCG_02150 with farnesyl diphosphate (1, FPP) gave (−)-δ-cadinene (2) while recombinant SSCG_03688 converted FPP to (+)-T-muurolol (3). Individual incubations of (−)-δ-cadinene synthase with [1,1-2H2]FPP (1a), (1S)-[1-2H]-FPP (1b), and (1R)-[1-2H]-FPP (1c) and NMR analysis of the resulting samples of deuterated (−)-δ-cadinene supported a cyclization mechanism involving the intermediacy of nerolidyl diphosphate (4) leading to a helminthogermacradienyl cation 5. Following a 1,3-hydride shift of the original H-1si of FPP, cyclization and deprotonation will give (−)-δ-cadinene. Similar incubations with recombinant SSCG_03688 supported an analogous mechanism for the formation of (+)-T-muurolol (3), also involving a 1,3-hydride shift of the original H-1siof FPP.

The terpene synthase encoded by the sav76 gene of Streptomyces avermtilis was expressed in Escherichia coli as an N-terminal-His6-tag protein, using a codon-optimized synthetic gene. Incubation of the recombinant protein, SAV_76, with farnesyl diphosphate (1, FPP) in the presence of Mg2+ gave a new sesquiterpene alcohol avermitilol (2), whose structure and stereochemistry were determined by a combination of 1H, 13C, COSY, HMQC, HMBC, and NOESY NMR, along with minor amounts of germacrene A (3), germacrene B (4), and viridiflorol (5). The absolute configuration of 2 was assigned by 1H NMR analysis of the corresponding (R) and (S)-Mosher esters. The steady state kinetic parameters were kcat 0.040 ± 0.001 s−1 and Km 1.06 ± 0.11 μM. Individual incubations of recombinant avermitilol synthase with [1,1-2H2]FPP (1a), (1S)-[1-2H]-FPP (1b), and (1R)-[1-2H]-FPP (1c) and NMR analysis of the resulting avermitilols supported a cyclization mechanism involving the loss of H-1re to generate the intermediate bicyclogermacrene (7), which then undergoes proton-initiated anti-Markovnikov cyclization and capture of water to generate 2. A copy of the sav76 gene was reintroduced into S. avermitilis SUKA17, a large deletion mutant from which the genes for the major endogenous secondary metabolites had been removed, and expressed under control of the of the native S. avermitilis promoter rpsJp (sav4925). The resultant transformants generated avermitilol (2) as well as the derived ketone, avermitilone (8), along with small amounts of 3, 4, and 5. The biochemical function of all four terpene synthases found in the S. avermtilis genome have now been determined.