Inhibition of Membrane-Active Peptides by Fatty Acid–Peptide Hybrids

Nine fatty acid–peptide hybrid molecules were constructed using the general formula CH₃(CH₂) _n CO-Phe Asp Cys-amide and tested for their ability to inhibit cell lysis induced by the membrane-active peptide melittin. All of these molecules, where n = 4–14, inhibited the action of melittin to some extent, but the longer carbon chains were most effective. Several potential inhibitors were also constructed with conservative substitutions in the peptide portion of the molecule. All were effective to varying degrees. We concluded that in the hexapeptide inhibitor published by Blondelle et al. (1993), the role of the first three residues is only to provide hydrophobic interaction with the melittin and has no particular amino acid sequence specificity. Some of these inhibitors were found to inhibit the lytic activity of a melittin analogue which had only superficial sequence similarity to melittin and also a truncated form of melittin, indicating the generality of the action of the inhibitors.Deceased 5/4/98     

Praying for Drought: Persistent Vulnerability and the Politics of Patronage in Ceará, Northeast Brazil

ABSTRACT   The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship.     

Penicillin-binding proteins 4 and 5 of Haemophilus influenzae are involved in cell wall incorporation

Abstract Permeabilized cells of Haemophilus influenzae incorporate wall precursors into murein material in an ampicillin-sensitive reaction. In resistant transformants that contain the low antibiotic affinity penicillin-binding proteins (PBPs) 4 and 5, the sensitivity of this incorporation reaction to ampicillin is proportionally lower, suggesting a catalytic role for these proteins in wall synthesis. We conclude that, analogous to the reaction in Escherichia coli , PBPs 4 and 5 of H. influenzae have transpeptidase activity.     

Lysine biosynthesis inMethanobacterium thermoautotrophicum is by the diaminopimelic acid pathway

Methanobacterium thermoautotrophicum, an archaebacterium, possesses the first and last enzymes of the diaminopimelic acid pathway for lysine biosynthesis, dihydrodipicolinate synthase, and diaminopimelate decarboxylase. It does not have saccharopine dehydrogenase, the last enzyme of the aminoadipate pathway for lysine biosynthesis. The dihydrodipicolinate synthase is inhibited but not repressed by lysine. We conclude that this microbe uses the diaminopimelate pathway for synthesis of lysine.Deceased.     

Functional rarefaction: estimating functional diversity from field data

Studies in biodiversity-ecosystem function and conservation biology have led to the development of diversity indices that take species' functional differences into account. We identify two broad classes of indices: those that monotonically increase with species richness (MSR indices) and those that weight the contribution of each species by abundance or occurrence (weighted indices). We argue that weighted indices are easier to estimate without bias but tend to ignore information provided by rare species. Conversely, MSR indices fully incorporate information provided by rare species but are nearly always underestimated when communities are not exhaustively surveyed. This is because of the well-studied fact that additional sampling of a community may reveal previously undiscovered species. We use the rarefaction technique from species richness studies to address sample-size-induced bias when estimating functional diversity indices. Rarefaction transforms any given MSR index into a family of unbiased weighted indices, each with a different level of sensitivity to rare species. Thus rarefaction simultaneously solves the problem of bias and the problem of sensitivity to rare species. We present formulae and algorithms for conducting a functional rarefaction analysis of the two most widely cited MSR indices: functional attribute diversity (FAD) and Petchey and Gaston's functional diversity (FD). These formulae also demonstrate a relationship between three seemingly unrelated functional diversity indices: FAD, FD and Rao's quadratic entropy. Statistical theory is also provided in order to prove that all desirable statistical properties of species richness rarefaction are preserved for functional rarefaction.     

Affinity labeling of dihydrofolate reductase with an antifolate glyoxal

Dihydrofolate reductases from different species contain several highly conserved arginines, some of which have been shown by x-ray crystallography to have their guanido groups near the p-aminobenzoyl glutamate moiety of enzyme-bound methotrexate. The orientation of one of these (Arg-52) appears to be completely reversed in comparing the crystal structures of Escherichia coli with Lactobacillus casei enzyme (Bolin, J. T., Filman, D. J., Matthews, D. A., Hamlin, R. C., and Kraut, J. (1982). J. Biol. Chem. 257, 13650-13662). We synthesized a novel antifolate containing a glyoxal group designed to react specifically with active-site guanido groups which are able to approach the p-aminobenzoyl carbonyl of methotrexate. The binding of this compound to the enzyme was competitive with dihydrofolate (DHF) in ordinary buffers. In borate buffer at pH 8.0 it inactivated dihydrofolate reductases from both E. coli and L. casei at similar maximum rates, while the chicken liver enzyme was more slowly inactivated. The inactivation was stoichiometric, paralleled the loss of the glyoxal chromophore, and showed saturation kinetics. Inhibitor binding and thus inactivation was enhanced by NADPH, while DHF protected the enzyme. This allowed calculation of the Kd for DHF which was found to be identical with its Km. The stoichiometrically inactivated enzyme displayed the 340-nm chromophore characteristic of 4-aminopteridines bound to dihydrofolate reductase confirming active-site labeling with normal orientation of the ligand. The ligand remained covalently bound to inactivated enzyme upon denaturation at low pH but dissociated at neutral pH. Computer graphic modeling of the crystal structures predicted reaction of Arg-31 but not Arg-52 in L. casei dihydrofolate reductase and of only Arg-52 in the E. coli enzyme. Purification of the CNBr fragments from the inactivated enzymes gave a single labeled peptide for each species. The particular peptide tagged in each case was unaffected by the presence of NADPH and was in excellent agreement with the crystallographic predictions.