SUMMARY
Measurements of the chitin content of the rooting horizons of a typical mor-humus heathland soil, indicate that chitin can contain in excess of 20% of the total nitrogen in the litter (L) horizon and 30% in the fermentation (F) horizon. Much of this chitin-nitrogen is thought to be contained in the mycelial walls of soil fungi.

Experiments were therefore designed to test the hypothesis that such sources of N could be rendered accessible to the ericaceous plants by their fungal endophytes. Mycelium of the ericoid endophyte Hymenoscyphus ericae (Read) Korf & Kernan and of the ectomycorrhizal fungus Suillus bovinus (Fr.) O. Krantze were grown in liquid culture before being killed and added either in the intact condition, or after fractionation, as sole sources of N to sterile media upon which were grown H. ericae in pure culture, or mycorrhizal and non-mycorrhizal plants of Vaccinium macrocarpon Ait. and Calluna vulgaris L. The abilities of the test organisms to utilize the nitrogen contained in the intact mycelial necromass, or in its fractions, were assessed by determining their yields and nitrogen concentrations of their tissues.

It was revealed that H. ericae was able to produce significantly higher yield when grown on intact fungal necromass than when provided with equivalent concentrations of N in the form of ammonium. Its yields on mycelial fractions were lower, but still significantly greater than those obtained in the controls lacking N. Significantly greater yields and N contents were also found in the ericaceous plants grown with these nitrogenous substrates in the mycorrhizal condition. Without H. ericae they had no access to the substrates. The possible ecological implications of these results are discussed.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1973.tb02110.x

The biology of mycorrhiza in the Ericaceae

Summary: Enormous efforts have been made to produce a protective vaccine against human immunodeficiency virus type 1; there has been little success. However, the identification of broadly neutralizing antibodies against epitopes on the highly conserved membrane-proximal external region (MPER) of the gp41 envelope protein has delineated this region as an attractive vaccine target. Furthermore, emerging structural information on the MPER has provided vaccine designers with new insights for building relevant immunogens. This review describes the current state of the field regarding (i) the structure and function of the gp41 MPER; (ii) the structure and binding mechanisms of the broadly neutralizing antibodies 2F5, 4E10, and Z13; and (iii) the development of an MPER-targeting vaccine. In addition, emerging approaches to vaccine design are presented.

The Membrane-Proximal External Region of the Human Immunodeficiency Virus Type 1 Envelope: Dominant Site of Antibody Neutralization and Target for Vaccine Design

Induction of effective antibody responses against HIV-1 infection remains an elusive goal for vaccine development. Progress may require in-depth understanding of the molecular mechanisms of neutralization by monoclonal antibodies. We have analyzed the molecular actions of two rare, broadly neutralizing, human monoclonal antibodies, 4E10 and 2F5, which target the transiently exposed epitopes in the membrane proximal external region (MPER) of HIV-1 gp41 envelope during viral entry. Both have long CDR H3 loops with a hydrophobic surface facing away from the peptide epitope. We find that the hydrophobic residues of 4E10 mediate a reversible attachment to the viral membrane and that they are essential for neutralization, but not for interaction with gp41. We propose that these antibodies associate with the viral membrane in a required first step and are thereby poised to capture the transient gp41 fusion intermediate. These results bear directly on strategies for rational design of HIV-1 envelope immunogens.

https://www.pnas.org/content/pnas/106/48/20234.full.pdf

Role of HIV membrane in neutralization by two broadly neutralizing antibodies

We tested the in vitro susceptibility of Candida albicans to three defensins from human neutrophilic granulocytes (HNP-1, 2, and 3), a homologous defensin from rabbit leukocytes (NP-1), and four unrelated cationic peptides. Although the primary amino acid sequences of HNP-1, 2, and 3 are identical except for a single amino-terminal amino acid alteration, HNP-1 and HNP-2 killed C. albicans but HNP-3 did not. C. albicans blastoconidia were protected from HNP-1 when incubations were performed in the absence of oxygen or in the presence of inhibitors that blocked both of its mitochondrial respiratory pathways. Neither anaerobiosis nor mitochondrial inhibitors substantially protected C. albicans exposed to NP-1, poly-L-arginine, poly-L-lysine, or mellitin. Human neutrophilic granulocyte defensin-mediated candidacidal activity was inhibited by both Mg2+ and Ca2+, and was unaffected by Fe2+. In contrast, Fe2+ inhibited the candidacidal activity of NP-1 and all of the model cationic peptides, whereas Mg2+ inhibited none of them. These data demonstrate that susceptibility of C. albicans to human defensins depends both on the ionic environment and on the metabolic state of the target cell. The latter finding suggests that leukocyte-mediated microbicidal mechanisms may manifest oxygen dependence for reasons unrelated to the production of reactive oxygen intermediates by the leukocyte.

/pdf/modulation-of-the-in-vitro-candidacidal-activity-of-human-1ed5sdczqd.pdf

Modulation of the in vitro candidacidal activity of human neutrophil defensins by target cell metabolism and divalent cations.

Chapter 16 – Carboxylesterases and Amidases

Utilization of methionine-containing peptides and their derivatives by a methionine-requiring auxotroph of Saccharomyces cerevisiae.

The HIV-1 envelope glycoprotein gp41 is responsible for viral fusion with the host cell. The fusion process, as well as the full structure of gp41, is not completely understood. One of the stronges...

The 2F5 epitope is helical in the HIV-1 entry inhibitor T-20.

Peptide utilization in yeast. Studies on methionine and lysine auxotrophs of Saccharomyces cerevisiae.

Permeation and stereospecificity of hydrolysis of peptide esters within intact lysosomes in vitro

The use of bromoacetyl derivatives in the determination of structure-function relationships in proteins is reviewed. Specific attention is paid to the advantages of the bromoacetyl functional group in the design and synthesis of active-site-directed reagents. Modification studies on staphylococcal nuclease and myeloma protein 315C are discussed in detail. Reagents containing the bromoacetyl group at prescribed distances from the binding center of the affinity label are described. Information gained from these studies gives insight into the spatial orientation of the amino acid side chains near the active sites of proteins.

Fred Naider

Papers

Utilization of methionine-containing peptides and their derivatives by a methionine-requiring auxotroph of Saccharomyces cerevisiae.

The 2F5 epitope is helical in the HIV-1 entry inhibitor T-20.

Peptide utilization in yeast. Studies on methionine and lysine auxotrophs of Saccharomyces cerevisiae.

Permeation and stereospecificity of hydrolysis of peptide esters within intact lysosomes in vitro

The Use of Bromoacetyl Derivatives for the Affinity Labeling of Proteins