Encounter with New Resources Causes Polarized Growth of the Cord-Forming Basidiomycete Phanerochaete velutina on Soil

Abstract The development and physiology of cord-forming saprotrophic basidiomycetes, which form extensive and persistent mycelial networks in woodland ecosystems, can be conveniently studied on non-sterile soil in laboratory microcosms mimicking field conditions. Morphological responses of Phanerochaete velutina mycelial systems to resource encounters, and decay partitioning following encounters, varied according to whether simulated woody litter was unsterile or autoclaved and on whether encounter took place at the mycelial foraging front or behind the margin (simulating litter fall onto established systems in the field). Results show that encounter of discrete resources by P. velutina is rapidly communicated to the entire mycelial system; that resource capture takes high priority at the expense of continued system extension and decay-derived carbon reallocation; and that polarized growth toward newly encountered resources, previously considered to occur infrequently with this species, may be readily detected using image analysis techniques. Potential advantages of polarized development of P. velutina are discussed.     

Strong Enrichment of Aromatic Residues in Binding Sites from a Charge-neutralized Hyperthermostable Sso7d Scaffold Library

The Sso7d protein from the hyperthermophilic archaeon Sulfolobus solfataricus is an attractive binding scaffold because of its small size (7 kDa), high thermal stability (T_m of 98 °C), and absence of cysteines and glycosylation sites. However, as a DNA-binding protein, Sso7d is highly positively charged, introducing a strong specificity constraint for binding epitopes and leading to nonspecific interaction with mammalian cell membranes. In the present study, we report charge-neutralized variants of Sso7d that maintain high thermal stability. Yeast-displayed libraries that were based on this reduced charge Sso7d (rcSso7d) scaffold yielded binders with low nanomolar affinities against mouse serum albumin and several epitopes on human epidermal growth factor receptor. Importantly, starting from a charge-neutralized scaffold facilitated evolutionary adaptation of binders to differentially charged epitopes on mouse serum albumin and human epidermal growth factor receptor, respectively. Interestingly, the distribution of amino acids in the small and rigid binding surface of enriched rcSso7d-based binders is very different from that generally found in more flexible antibody complementarity-determining region loops but resembles the composition of antibody-binding energetic hot spots. Particularly striking was a strong enrichment of the aromatic residues Trp, Tyr, and Phe in rcSso7d-based binders. This suggests that the rigidity and small size of this scaffold determines the unusual amino acid composition of its binding sites, mimicking the energetic core of antibody paratopes. Despite the high frequency of aromatic residues, these rcSso7d-based binders are highly expressed, thermostable, and monomeric, suggesting that the hyperstability of the starting scaffold and the rigidness of the binding surface confer a high tolerance to mutation.     

(+/-)2,3-Dihydroxypropyl dichloroacetate, an inhibitor of glycerol kinase

Of a range of glycerol analogues, (+/-)-2,3-dihydroxypropyl dichloroacetate (III) has been shown to be the most potent inhibitor of glycerol kinase in vitro. Inhibition is noncompetitive with a Ki value of 1.8 X 10(-3) M. The presence of ATP seems essential for effective inhibition of the enzyme, suggesting that the inhibitor is phosphorylated to a glycerol-3-phosphate analogue. In vivo III causes a decrease in the specific activity of liver glycerol kinase and produces a dose-dependent reduction in blood glucose levels. There is a reduction in the conversion of [U-14C] glycerol into glucose after administration of III to CBA/CA mice while gluconeogenesis from fructose is increased. This suggests that of the enzymes of gluconeogenesis only glycerol kinase is inhibited by III. This compound may be useful in reducing the lipid contribution to gluconeogenesis in advancing cancer.     

Enzymatic methylation of cytosine in DNA is prevented by adjacent O6-methylguanine residues

The effect of O6-alkylation of guanine residues on the enzymic methylation of cytosine has been studied using synthetic oligonucleotides in which all guanines in cytosine-guanine sequences at potentially methylatable sites are replaced by O6-methylguanine. In contrast with the unmodified forms, which showed high acceptance activity for methyl-3H-labeled groups from S-adenosyl-L-[methyl-3H]methionine in the presence of DNA methylase, the modified oligonucleotides were not substrates for the enzyme either in the single-stranded or annealed forms. In view of the importance of cytosine methylation in the down-regulation of certain genes, the potential to affect gene expression by this mechanism may be a contributory factor in the toxic and carcinogenic effects of chemical methylating agents.