Body Composition in Advanced Non-Small Cell Lung Cancer Treated With Immunotherapy.

Importance: The association between body composition (BC) and cancer outcomes is complex and incompletely understood. Previous research in non-small-cell lung cancer (NSCLC) has been limited to small, single-institution studies and yielded promising, albeit heterogeneous, results. Objectives: To evaluate the association of BC with oncologic outcomes in patients receiving immunotherapy for advanced or metastatic NSCLC. Design, Setting, and Participants: This comprehensive multicohort analysis included clinical data from cohorts receiving treatment at the Dana-Farber Brigham Cancer Center (DFBCC) who received immunotherapy given alone or in combination with chemotherapy and prospectively collected data from the phase 1/2 Study 1108 and the chemotherapy arm of the phase 3 MYSTIC trial. Baseline and follow-up computed tomography (CT) scans were collected and analyzed using deep neural networks for automatic L3 slice selection and body compartment segmentation (skeletal muscle [SM], subcutaneous adipose tissue [SAT], and visceral adipose tissue). Outcomes were compared based on baseline BC measures or their change at the first follow-up scan. The data were analyzed between July 2022 and April 2023. Main Outcomes and Measures: Hazard ratios (HRs) for the association of BC measurements with overall survival (OS) and progression-free survival (PFS). Results: A total of 1791 patients (878 women [49%]) with NSCLC were analyzed, of whom 487 (27.2%) received chemoimmunotherapy at DFBCC (DFBCC-CIO), 825 (46.1%) received ICI monotherapy at DFBCC (DFBCC-IO), 222 (12.4%) were treated with durvalumab monotherapy on Study 1108, and 257 (14.3%) were treated with chemotherapy on MYSTIC; median (IQR) ages were 65 (58-74), 66 (57-71), 65 (26-87), and 63 (30-84) years, respectively. A loss in SM mass, as indicated by a change in the L3 SM area, was associated with worse oncologic outcome across patient groups (HR, 0.59 [95% CI, 0.43-0.81] and 0.61 [95% CI, 0.47-0.79] for OS and PFS, respectively, in DFBCC-CIO; HR, 0.74 [95% CI, 0.60-0.91] for OS in DFBCC-IO; HR, 0.46 [95% CI, 0.33-0.64] and 0.47 [95% CI, 0.34-0.64] for OS and PFS, respectively, in Study 1108; HR, 0.76 [95% CI, 0.61-0.96] for PFS in the MYSTIC trial). This association was most prominent among male patients, with a nonsignificant association among female patients in the MYSTIC trial and DFBCC-CIO cohorts on Kaplan-Meier analysis. An increase of more than 5% in SAT density, as quantified by the average CT attenuation in Hounsfield units of the SAT compartment, was associated with poorer OS in 3 patient cohorts (HR, 0.61 [95% CI, 0.43-0.86] for DFBCC-CIO; HR, 0.62 [95% CI, 0.49-0.79] for DFBCC-IO; and HR, 0.56 [95% CI, 0.40-0.77] for Study 1108). The change in SAT density was also associated with PFS for DFBCC-CIO (HR, 0.73; 95% CI, 0.54-0.97). This was primarily observed in female patients on Kaplan-Meier analysis. Conclusions and Relevance: The results of this multicohort study suggest that loss in SM mass during systemic therapy for NSCLC is a marker of poor outcomes, especially in male patients. SAT density changes are also associated with prognosis, particularly in female patients. Automated CT-derived BC measurements should be considered in determining NSCLC prognosis.

ASCT2-Targeting Antibody-Drug Conjugate MEDI7247 in Adult Patients with Relapsed/Refractory Hematological Malignancies: A First-in-Human, Phase 1 Study.

BACKGROUND: MEDI7247 is a first-in-class antibody-drug conjugate (ADC) consisting of an anti-sodium-dependent alanine-serine-cysteine transporter 2 antibody-conjugated to a pyrrolobenzodiazepine dimer. OBJECTIVE: This first-in-human phase 1 trial evaluated MEDI7247 in patients with hematological malignancies. PATIENTS AND METHODS: Adults with acute myeloid leukemia (AML), multiple myeloma (MM), or diffuse large B-cell lymphoma (DLBCL) relapsed or refractory (R/R) to standard therapies, or for whom no standard therapy exists, were eligible. Primary endpoints were safety and determination of the maximum tolerated dose (MTD). Secondary endpoints included assessments of antitumor activity, pharmacokinetics (PK), and immunogenicity. RESULTS: As of 26 March 2020, 67 patients were treated (AML: n = 27; MM: n = 18; DLBCL: n = 22). The most common MEDI7247-related adverse events (AEs) were thrombocytopenia (41.8%), neutropenia (35.8%), and anemia (28.4%). The most common treatment-related grade 3/4 AEs were thrombocytopenia (38.8%), neutropenia (34.3%), and anemia (22.4%). Anticancer activity (number of responders/total patients evaluated) was observed in 11/67 (16.4%) patients. No correlation was observed between ASCT2 expression and clinical response. Between-patient variability of systemic exposure of MEDI7247 ADC and total antibody were high (AUCinf geometric CV%: 62.3-134.2, and 74.8-126.1, respectively). SG3199 (PBD dimer) plasma concentrations were below the limit of quantification for all patients after Study Day 8. Anti-drug antibody (ADA) prevalence was 7.7%, ADA incidence was 1.9%, and persistent-positive ADA was 5.8%. CONCLUSIONS: Thrombocytopenia and neutropenia limited repeat dosing. Although limited clinical activity was detected, the dose-escalation phase was stopped early without establishing an MTD. The study was registered with ClinicalTrials.gov (NCT03106428).

HIV-1 Matrix Trimerization-Impaired Mutants Are Rescued by Matrix Substitutions That Enhance Envelope Glycoprotein Incorporation.

The matrix (MA) domain of HIV-1 Gag plays key roles in virus assembly by targeting the Gag precursor to the plasma membrane and directing the incorporation of the viral envelope (Env) glycoprotein into virions. The latter function appears to be in part dependent on trimerization of the MA domain of Gag during assembly, as disruption of the MA trimer interface impairs Env incorporation. Conversely, many MA mutations that impair Env incorporation can be rescued by compensatory mutations in the trimer interface. In this study, we sought to investigate further the biological significance of MA trimerization by isolating and characterizing compensatory mutations that rescue MA trimer interface mutants with severely impaired Env incorporation. By serially propagating MA trimerization-defective mutants in T cell lines, we identified a number of changes in MA, both within and distant from the trimer interface. The compensatory mutations located within or near the trimer interface restored Env incorporation and particle infectivity and permitted replication in culture. The structure of the MA lattice was interrogated by measuring the cleavage of the murine leukemia virus (MLV) transmembrane Env protein by the viral protease in MLV Env-pseudotyped HIV-1 particles bearing the MA mutations and by performing crystallographic studies of in vitro-assembled MA lattices. These results demonstrate that rescue is associated with structural alterations in MA organization and rescue of MA domain trimer formation. Our data highlight the significance of the trimer interface of the MA domain of Gag as a critical site of protein-protein interaction during HIV-1 assembly and establish the functional importance of trimeric MA for Env incorporation.IMPORTANCE The immature Gag lattice is a critical structural feature of assembling HIV-1 particles, which is primarily important for virion formation and release. While Gag forms a hexameric lattice, driven primarily by the capsid domain, the MA domain additionally trimerizes where three Gag hexamers meet. MA mutants that are defective for trimerization are deficient for Env incorporation and replication, suggesting a requirement for trimerization of the MA domain of Gag in Env incorporation. This study used a gain-of-function, forced viral evolution approach to rescue HIV-1 mutants that are defective for MA trimerization. Compensatory mutations that rescue virus replication do so by restoring Env incorporation and MA trimer formation. This study supports the importance of MA domain trimerization in HIV-1 replication and the potential of the trimer interface as a therapeutic target.

Integrated Genomic, Epigenomic, and Expression Analyses of Ovarian Cancer Cell Lines.

To improve our understanding of ovarian cancer, we performed genome-wide analyses of 45 ovarian cancer cell lines. Given the challenges of genomic analyses of tumors without matched normal samples, we developed approaches for detection of somatic sequence and structural changes and integrated these with epigenetic and expression alterations. Alterations not previously implicated in ovarian cancer included amplification or overexpression of ASXL1 and H3F3B, deletion or underexpression of CDC73 and TGF-beta receptor pathway members, and rearrangements of YAP1-MAML2 and IKZF2-ERBB4. Dose-response analyses to targeted therapies revealed unique molecular dependencies, including increased sensitivity of tumors with PIK3CA and PPP2R1A alterations to PI3K inhibitor GNE-493, MYC amplifications to PARP inhibitor BMN673, and SMAD3/4 alterations to MEK inhibitor MEK162. Genome-wide rearrangements provided an improved measure of sensitivity to PARP inhibition. This study provides a comprehensive and broadly accessible resource of molecular information for the development of therapeutic avenues in ovarian cancer.

DNA Methylation Patterns Separate Senescence from Transformation Potential and Indicate Cancer Risk.

Overall shared DNA methylation patterns between senescence (Sen) and cancers have led to the model that tumor-promoting epigenetic patterns arise through senescence. We show that transformation-associated methylation changes arise stochastically and independently of programmatic changes during senescence. Promoter hypermethylation events in transformation involve primarily pro-survival and developmental genes, similarly modified in primary tumors. Senescence-associated hypermethylation mainly involves metabolic regulators and appears early in proliferating "near-senescent" cells, which can be immortalized but are refractory to transformation. Importantly, a subset of transformation-associated hypermethylated developmental genes exhibits highest methylation gains at all age-associated cancer risk states across tissue types. These epigenetic changes favoring cell self-renewal and survival, arising during tissue aging, are fundamentally important for stratifying cancer risk and concepts for cancer prevention.

A KDM5 Inhibitor Increases Global H3K4 Trimethylation Occupancy and Enhances the Biological Efficacy of 5-Aza-2'-Deoxycytidine.

The H3K4 demethylase KDM5B is amplified and overexpressed in luminal breast cancer, suggesting it might constitute a potential cancer therapy target. Here, we characterize, in breast cancer cells, the molecular effects of a recently developed small-molecule inhibitor of the KDM5 family of proteins (KDM5i), either alone or in combination with the DNA-demethylating agent 5-aza-2'-deoxycytidine (DAC). KDM5i treatment alone increased expression of a small number of genes, whereas combined treatment with DAC enhanced the effects of the latter for increasing expression of hundreds of DAC-responsive genes. ChIP-seq studies revealed that KDM5i resulted in the broadening of existing H3K4me3 peaks. Furthermore, cells treated with the drug combination exhibited increased promoter and gene body H3K4me3 occupancy at DAC-responsive genes compared with DAC alone. Importantly, treatment with either DAC or DAC+KDM5i induced a dramatic increase in H3K27ac at enhancers with an associated significant increase in target gene expression, suggesting a previously unappreciated effect of DAC on transcriptional regulation. KDM5i synergized with DAC to reduce the viability of luminal breast cancer cells in in vitro assays. Our study provides the first look into the molecular effects of a novel KDM5i compound and suggests that combinatorial inhibition along with DAC represents a new area to explore in translational epigenetics.Significance: This study offers a first look into the molecular effects of a novel KDM5 inhibitory compound, suggesting how its use in combination with DNA methylation inhibitors presents new opportunities to explore in translational cancer epigenetics. Cancer Res; 78(5); 1127-39. ©2017 AACR.

Chronic Cigarette Smoke-Induced Epigenomic Changes Precede Sensitization of Bronchial Epithelial Cells to Single-Step Transformation by KRAS Mutations.

We define how chronic cigarette smoke-induced time-dependent epigenetic alterations can sensitize human bronchial epithelial cells for transformation by a single oncogene. The smoke-induced chromatin changes include initial repressive polycomb marking of genes, later manifesting abnormal DNA methylation by 10 months. At this time, cells exhibit epithelial-to-mesenchymal changes, anchorage-independent growth, and upregulated RAS/MAPK signaling with silencing of hypermethylated genes, which normally inhibit these pathways and are associated with smoking-related non-small cell lung cancer. These cells, in the absence of any driver gene mutations, now transform by introducing a single KRAS mutation and form adenosquamous lung carcinomas in mice. Thus, epigenetic abnormalities may prime for changing oncogene senescence to addiction for a single key oncogene involved in lung cancer initiation.

Targeting hexokinase 2 inhibition promotes radiosensitization in HPV16 E7-induced cervical cancer and suppresses tumor growth.

In order to improve the sensitivity of cervical cancer cells to irradiation therapy, we targeted hexokinase 2 (HK2), the first rate-limiting enzyme of glycolysis, and explore its role in cervical cancer cells. We suppressed HK2 expression and/or function by shRNA and/or metformin and found HK2 inhibition enhanced cells apoptosis with accelerating expression of cleaved PARP and caspase-3. HK2 inhibition also induced much inferior proliferation of cervical cancer cells both in vitro and in vivo with diminishing expression of mTOR, MIB and MGMT. Moreover, HK2 inhibition altered the metabolic profile of cervical cancer cells to one less dependent on glycolysis with a reinforcement of mitochondrial function and an ablation of lactification ability. Importantly, cervical cancer cells contained HK2 inhibition displayed more sensitivity to irradiation. Further results indicated that HPV16 E7 oncoprotein altered the glucose homeostasis of cervical cancer cells into glycolysis by coordinately promoting HK2 expression and its downregulation of glycolysis. Taken together, our findings supported a mechanism whereby targeting HK2 inhibition contributed to suppress HPV16 E7-induced tumor glycolysis metabolism phenotype, inhibiting tumor growth, and induced apoptosis, blocking the cancer cell energy sources and ultimately enhanced the sensitivity of HPV(+) cervical cancer cells to irradiation therapy.

Bolaamphiphiles as carriers for siRNA delivery: From chemical syntheses to practical applications.

In this study we have investigated a new class of cationic lipids--"bolaamphiphiles" or "bolas"--for their ability to efficiently deliver small interfering RNAs (siRNAs) to cancer cells. The bolas of this study consist of a hydrophobic chain with one or more positively charged head groups at each end. Recently, we reported that micelles of the bolas GLH-19 and GLH-20 (derived from vernonia oil) efficiently deliver siRNAs, while having relatively low toxicities in vitro and in vivo. Our previous studies validated that; bolaamphiphiles can be designed to vary the magnitude of siRNA shielding, its delivery, and its subsequent release. To further understand the structural features of bolas critical for siRNAs delivery, new structurally related bolas (GLH-58 and GLH-60) were designed and synthesized from jojoba oil. Both bolas have similar hydrophobic domains and contain either one, in GLH-58, or two, in GLH-60 positively charged head groups at each end of the hydrophobic core. We have computationally predicted and experimentally validated that GLH-58 formed more stable nano sized micelles than GLH-60 and performed significantly better in comparison to GLH-60 for siRNA delivery. GLH-58/siRNA complexes demonstrated better efficiency in silencing the expression of the GFP gene in human breast cancer cells at concentrations of 5µg/mL, well below the toxic dose. Moreover, delivery of multiple different siRNAs targeting the HIV genome demonstrated further inhibition of virus production.

Triggering of RNA interference with RNA-RNA, RNA-DNA, and DNA-RNA nanoparticles.

Control over cellular delivery of different functionalities and their synchronized activation is a challenging task. We report several RNA and RNA/DNA-based nanoparticles designed to conditionally activate the RNA interference in various human cells. These nanoparticles allow precise control over their formulation, stability in blood serum, and activation of multiple functionalities. Importantly, interferon and pro-inflammatory cytokine activation assays indicate the significantly lower responses for DNA nanoparticles compared to the RNA counterparts, suggesting greater potential of these molecules for therapeutic use.

The griffithsin dimer is required for high-potency inhibition of HIV-1: evidence for manipulation of the structure of gp120 as part of the griffithsin dimer mechanism.

Griffithsin (Grft) is a protein lectin derived from red algae that tightly binds the HIV envelope protein gp120 and effectively inhibits virus infection. This inhibition is due to the binding by Grft of high-mannose saccharides on the surface of gp120. Grft has been shown to be a tight dimer, but the role of the dimer in Grft's anti-HIV function has not been fully explored. To investigate the role of the Grft dimer in anti-HIV function, an obligate dimer of Grft was designed by expressing the protein with a peptide linker between the two subunits. This "Grft-linker-Grft" is a folded protein dimer, apparently nearly identical in structural properties to the wild-type protein. A "one-armed" obligate dimer was also designed (Grft-linker-Grft OneArm), with each of the three carbohydrate binding sites of one subunit mutated while the other subunit remained intact. While both constructed dimers retained the ability to bind gp120 and the viral surface, Grft-linker-Grft OneArm was 84- to 1,010-fold less able to inhibit HIV than wild-type Grft, while Grft-linker-Grft had near-wild-type antiviral potency. Furthermore, while the wild-type protein demonstrated the ability to alter the structure of gp120 by exposing the CD4 binding site, Grft-linker-Grft OneArm largely lost this ability. In experiments to investigate gp120 shedding, it was found that Grft has different effects on gp120 shedding for strains from subtype B and subtype C, and this might correlate with Grft function. Evidence is provided that the dimer form of Grft is critical to the function of this protein in HIV inhibition.

The role of individual carbohydrate-binding sites in the function of the potent anti-HIV lectin griffithsin.

Griffithsin (GRFT) is a lectin that has been shown to inhibit HIV infection by binding to high mannose glycan structures on the surface of gp120, and it is among the most potent HIV entry inhibitors reported so far. However, important biochemical details on the antiviral mechanism of GRFT action remain unexplored. In order to understand the role of the three individual carbohydrate-binding sites (CBS) in GRFT, mutations were made at each site (D30A, D70A, and D112A), and the resulting mutants were investigated. NMR studies revealed that each GRFT variant was folded but showed significant peak movement on the carbohydrate-binding face of the protein. The wild-type and each point mutant protein appeared as tight dimers with a K(d) below 4.2 µM. Mutation of any individual CBS on GRFT reduced binding of the protein to mannose, and ELISA assays revealed a partial loss of ability of each GRFT point mutant to bind gp120, with a near-complete loss of binding by the triple mutant D30A/D70A/D112A GRFT. A more quantitative surface plasmon resonance (SPR) examination showed a rather small loss of binding to gp120 for the individual GRFT point mutants (K(D): 123 to 245 pM range versus 73 pM for wild-type GRFT), but dramatic loss of the triple mutant to bind gp120 derived from R5 and X4 strains (K(D) > 12 nM). In contrast to the 2- to 3-fold loss of binding to gp120, the single CBS point mutants of GRFT were significantly less able to inhibit viral infection, exhibiting a 26- to 1900-fold loss of potency, while the triple mutant was at least 875-fold less effective against HIV-1 infection. The disparity between HIV-1 gp120 binding ability and HIV inhibitory potency for these GRFT variants indicates that gp120 binding and virus neutralization do not necessarily correlate, and suggests a mechanism that is not based on simple gp120 binding.

Potent strategy to inhibit HIV-1 by binding both gp120 and gp41.

The development of an anti-HIV microbicide is critical in the fight against the spread of HIV. It is shown here that the covalent linking of compounds that bind gp120 with compounds that bind gp41 can inhibit HIV entry even more potently than individual inhibitors or noncovalent combinations. The most striking example involves griffithsin, a potent HIV inhibitor that binds to the surface of HIV gp120. While griffithsin inhibits HIV Env-mediated fusion in a CCR5-tropic cell-cell fusion assay with a 50% inhibitory concentration (IC(50)) of 1.31 ± 0.87 nM and the gp41-binding peptide C37 shows an IC(50) of 18.2 ± 7.6 nM, the covalently linked combination of griffithsin with C37 (Griff37) has an IC(50) of 0.15 ± 0.05 nM, exhibiting a potency 8.7-fold greater than that of griffithsin alone. Similarly, in CXCR4-tropic cell-cell fusion assays, Griff37 is 5.2-fold more potent than griffithsin alone. In viral assays, both griffithsin and Griff37 inhibit HIV replication at midpicomolar levels, but the linked compound Griff37 is severalfold more potent than griffithsin alone against both CCR5- and CXCR4-tropic virus strains. Another example of this strategy is the covalently linked combination of peptide C37 with a variant of the gp120-binding peptide CD4M33 (L. Martin et al., Nat. Biotechnol. 21:71-76, 2003). Also, nuclear magnetic resonance (NMR) spectra for several of these compounds are shown, including, to our knowledge, the first published NMR spectrum for griffithsin.

Structural and functional studies of the potent anti-HIV chemokine variant P2-RANTES.

The N-terminal region of the chemokine RANTES is critical for its function. A synthesized N-terminally modified analog of RANTES, P2-RANTES, was discovered using a phage display selection against living CCR5-expressing cells, and has been reported to inhibit HIV-1 env-mediated cell-cell fusion at subnanomolar levels (Hartley et al. J Virol 2003;77:6637-6644). In the present study we produced this protein using E. coli overexpression and extensively studied its structure and function. The x-ray crystal structure of P2-RANTES was solved and refined at 1.7 A resolution. This protein was found to be predominantly a monomer in solution by analytical ultracentrifugation, but a tetramer in the crystal. In studies of glycosaminoglycan binding, P2-RANTES was found to be significantly less able to bind heparin than wild type RANTES. We also tested this protein for receptor internalization where it was shown to be functional, in cell-cell fusion assays where recombinant P2-RANTES was a potent fusion inhibitor (IC(50) = 2.4 +/- 0.8 nM), and in single round infection assays where P2-RANTES inhibited at subnanomolar levels. Further, in a modified fusion assay designed to test specificity of inhibition, P2-RANTES was also highly effective, with a 65-fold improvement over the fusion inhibitor C37, which is closely related to the clinically approved inhibitor T-20. These studies provide detailed structural and functional information for this novel N-terminally modified chemokine mutant. This information will be very useful in the development of more potent anti-HIV agents. PDB Accession Number: 2vxw.

Conservation of unfavorable sequence motifs that contribute to the chemokine quaternary state.

In the chemokine family, we characterize two examples of evolutionarily conserved unfavorable sequence motifs that affect quaternary structure. In contrast to the straightforward action of favorable sequences, these unfavorable motifs produce interactions disfavoring one outcome to indirectly promote another one but should not be confused with the broad sampling produced by negative selection and/or design. To identify such motifs, we developed a statistically validated computational method combining structure and phylogeny. This approach was applied in an analysis of the alternate forms of homodimerization exhibited in the chemokine family. While the chemokine family exhibits the same tertiary fold, members of certain subfamilies, including CXCL8, form a homodimer across the beta1 strand whereas members of other subfamilies, including CCL4 and CCL2, form a homodimer on the opposite side of the chemokine fold. These alternate dimerization states suggest that CCL4 and CCL2 contain specific sequences that disfavor CXCL8 dimerization. Using our computational approach, we identified two evolutionarily conserved sequence motifs in the CC subfamilies: a drastic two-residue deletion (DeltaRV) and a simple point mutation (V27R). Cloned into the CXCL8 background, these two motifs were experimentally proven to confer a monomeric state. NMR analyses indicate that these variants are structured in solution and retain the chemokine fold. Structurally, the motifs retain a chemokine tertiary fold while introducing unfavorable quaternary interactions that inhibit CXCL8 dimerization. In demonstrating the success of our computational method, our results argue that these unfavorable motifs have been evolutionarily conserved to specifically disfavor one dimerization state and, as a result, indirectly contribute to favoring another.

An information measure of the quality of protein secondary structure prediction.

We describe an information-theory-based measure of the quality of secondary structure prediction (RELINFO). RELINFO has a simple yet intuitive interpretation: it represents the factor by which secondary structure choice at a residue has been restricted by a prediction scheme. As an alternative interpretation of secondary structure prediction, RELINFO complements currently used methods by providing an information-based view as to why a prediction succeeds and fails. To demonstrate this score's capabilities, we applied RELINFO to an analysis of a large set of secondary structure predictions obtained from the first five rounds of the Critical Assessment of Structure Prediction (CASP) experiment. RELINFO is compared with two other common measures: percent correct (Q3) and secondary structure overlap (SOV). While the correlation between Q3 and RELINFO is approximately 0.85, RELINFO avoids certain disadvantages of Q3, including overestimating the quality of a prediction. The correlation between SOV and RELINFO is approximately 0.75. The valuable SOV measure unfortunately suffers from a saturation problem, and perhaps has unfairly given the general impression that secondary structure prediction has reached its limit since SOV hasn't improved much over the recent rounds of CASP. Although not a replacement for SOV, RELINFO has greater dispersion. Over the five rounds of CASP assessed here, RELINFO shows that predictions targets have been more difficult in successive CASP experiments, yet the predictions quality has continued to improve measurably over each round. In terms of information, the secondary structure prediction quality has almost doubled from CASP1 to CASP5. Therefore, as a different perspective of accuracy, RELINFO can help to improve prediction of protein secondary structure by providing a measure of difficulty as well as final quality of a prediction.

Nickel-dependent oligomerization of the alpha subunit of acetyl-coenzyme a synthase/carbon monoxide dehydrogenase.

After activation with NiCl2, the recombinant alpha subunit of the Ni-containing alpha2beta2 acetyl-CoA synthase/carbon monoxide dehydrogenase (ACS/CODH) catalyzes the synthesis of acetyl-CoA from CO, CoA, and a methyl group donated from the corrinoid-iron-sulfur protein (CoFeSP). The alpha subunit has two conformations (open and closed), and contains a novel [Fe4S4]-[Nip Nid] active site in which the proximal Nip ion is labile. Prior to Ni activation, recombinant apo-alpha contain only an Fe4S4 cluster. Ni-activated alpha subunits exhibit catalytic, spectroscopic and heterogeneity properties typical of alpha subunits contained in ACS/CODH. Evidence presented here indicates that apo-alpha is a monomer whereas Ni-treated alpha oligomerizes, forming dimers and higher molecular weight species including tetramers. No oligomerization occurred when apo-alpha was treated with Cu(II), Zn(II), or Co(II) ions, but oligomerization occurred when apo-alpha was treated with Pt(II) and Pd(II) ions. The dimer accepted only 0.5 methyl group/alpha and exhibited, upon treatment with CO and under reducing conditions, the NiFeC EPR signal quantifying to 0.4 spin/alpha. Dimers appear to consist of two types of alpha subunits, including one responsible for catalytic activity and one that provides a structural scaffold. Higher molecular weight species may be similarly constituted. It is concluded that Ni binding to the A-cluster induces a conformational change in the alpha subunit, possibly to the open conformation, that promotes oligomerization. These interrelated events demonstrate previously unrealized connections between (a) the conformation of the alpha subunit; (b) the metal which occupies the proximal/distal sites of the A-cluster; and (c) catalytic activity.

Detecting protein dissimilarities in multiple alignments using Bayesian variable selection.

MOTIVATION: We present an application of Bayesian variable selection to the novel detection of sequence elements that confer negative design to protein structure and function. As an illustration, we analyze the different dimer interfaces between the CXCL8 chemokine family with the CCL4 and CCL2 chemokine families to discover the changes that disfavor CXCL8 of quaternary structure. RESULTS: In comparison with known experimental results, our method identifies evolutionarily conserved sequence changes in the CC families that inhibit CXCL8 quaternary structure. Therefore, we find positive selection of negative design elements. Furthermore, our approach predicts that a two-residue deletion conserved in the CCL4 chemokine family disfavors CXCL8 dimerization. AVAILABILITY: The Matlab code for the Bayesian variable selection is freely available at http://stat.tamu.edu/~mvannucci/webpages/codes.html

Sorghum bicolor's transcriptome response to dehydration, high salinity and ABA.

Genome wide changes in gene expression were monitored in the drought tolerant C4 cereal Sorghum bicolor, following exposure of seedlings to high salinity (150 mM NaCl), osmotic stress (20% polyethylene glycol) or abscisic acid (125 microM ABA). A sorghum cDNA microarray providing data on 12,982 unique gene clusters was used to examine gene expression in roots and shoots at 3- and 27-h post-treatment. Expression of approximately 2200 genes, including 174 genes with currently unknown functions, of which a subset appear unique to monocots and/or sorghum, was altered in response to dehydration, high salinity or ABA. The modulated sorghum genes had homology to proteins involved in regulation, growth, transport, membrane/protein turnover/repair, metabolism, dehydration protection, reactive oxygen scavenging, and plant defense. Real-time PCR was used to quantify changes in relative mRNA abundance for 333 genes that responded to ABA, NaCl or osmotic stress. Osmotic stress inducible sorghum genes identified for the first time included a beta-expansin expressed in shoots, actin depolymerization factor, inositol-3-phosphate synthase, a non-C4 NADP-malic enzyme, oleosin, and three genes homologous to 9-cis-epoxycarotenoid dioxygenase that may be involved in ABA biosynthesis. Analysis of response profiles demonstrated the existence of a complex gene regulatory network that differentially modulates gene expression in a tissue- and kinetic-specific manner in response to ABA, high salinity and water deficit. Modulation of genes involved in signal transduction, chromatin structure, transcription, translation and RNA metabolism contributes to sorghum's overlapping but nonetheless distinct responses to ABA, high salinity, and osmotic stress. Overall, this study provides a foundation of information on sorghum's osmotic stress responsive gene complement that will accelerate follow up biochemical, QTL and comparative studies.