Jens Freund

Human immunodeficiency virus type 2 (HIV-2) Nef is proteolytically cleaved by the HIV-2-encoded protease. The proteolysis is not influenced by the absence or presence of the N-terminal myristoylation. The main cleavage site is located between residues 39 and 40, suggesting a protease recognition sequence, GGEY-SQFQ. As observed previously for Nef protein from HIV-1, a large, stable core domain with an apparent molecular mass of 30 kDa is produced by the proteolytic activity. Cleavage of Nef from HIV-1 in two domains by its own protease or the protease from HIV-2 is also independent of Nef myristoylation. However, processing of HIV-1 Nef by the HIV-2 protease is less selective than that by the HIV-1 protease: the obtained core fragment is heterogeneous at its N terminus and has an additional cleavage site between amino acids 99 and 100. Preliminary experiments suggest that the full-length Nef of HIV-2 and the core domain are part of the HIV-2 particles, analogous to the situation rep...

In this article the author tries to sketch the most likely scenario of origin of life taken the facts known today into account. The main thesis is that early life already evolved during the time of disastrous meteorite impacts which nearly sterilized the whole Earth by boiling and evaporating most of the liquid water. This is in contrast to the usual unquestioned assumption that early life evolved after the meteorite bombardment of early Earth calmed down and stable oceans were present. The main reasons for this thesis are the unexpected uniformity of the genetic code, the two fundamentally different forms of cell membranes, the high evolution speed needed, and the energy rich molecules needed. Those reasons and the unlikelihood of other explanations (like extraterrestrial or autotrophic origin) are discussed in detail. The thesis presented here implies that life could only emerge during the meteorite bombardment and not after it ended. The much more speculative consequences are dis...

In this article the author tries to sketch the most likely scenario of origin of life taken the facts known today into account. The main thesis is that early life already evolved during the time of disastrous meteorite impacts which nearly sterilized the whole Earth by boiling and evaporating most of the liquid water. This is in contrast to the usual unquestioned assumption that early life evolved after the meteorite bombardment of early Earth calmed down and stable oceans were present. The main reasons for this thesis are the unexpected uniformity of the genetic code, the two fundamentally different forms of cell membranes, the high evolution speed needed, and the energy rich molecules needed. Those reasons and the unlikelihood of other explanations (like extraterrestrial or autotrophic origin) are discussed in detail. The thesis presented here implies that life could only emerge during the meteorite bombardment and not after it ended. Typically it is assumed that life emerges on a...

The solid phase synthesis of the inhibitor of hematopoietic stem cell proliferation, Ac–Ser–Asp–Lys–Pro–OH, and its derivative Ac–Ala–Asp–Lys–Pro–OH is described. 1H and 13C NMR investigations demonstrate that both peptides show no prefered conformation in water solution. Both peptides exist in a Pro-cis-trans equilibrium ratio of 9 (trans) : 1 (cis). Thymosin β4 is believed to be the precursor molecule of the tetrapeptide Ac–SDKP. The attachement of the random coil tetrapeptide to a rigid helical fragment could facilitate its in vivo enzymatic cleavage.

Proteolytic experiments in conjunction with 1H‐NMR spectroscopy show that the Nef (negative factor) protein from human immunodeficiency virus type 1 probably consists of two main domains, the N‐terminal anchor domain at amino acid positions 2–65 and the C‐terminal core domain at positions 66—206. The N‐terminal domain is likely to be located at the surface of the protein, while the C‐terminal domain has a compactly folded core and is stable in the absence of the anchor domain. It is conceivable that the core domain represents a functional domain of the Nef protein, activated after the removal of the membrane anchor by the human‐immunodeficiency‐virus protease or cellular proteases.Nef is stable at pH 5–12 and denatures at 317–322 K. The Nef protein remains in its native conformation in dimethyl‐sulfoxide/water mixtures up to 35% (by vol.), and in acetonitrile/water up to 14% (by vol.). Nef refolds spontaneously after denaturation with urea or guanidinium hydrochloride. The 1H‐NMR pa...

The nef genes, derived from two different human immunodeficiency‐virus‐type‐1 (HIV‐1) strains, were expressed in procaryotic cells (Escherichia coli) and in eucaryotic cells (insect cells infected with nef‐containing baculovirus). The oligomerization of recombinant Nef protein was studied by NMR spectroscopy and immunoblotting under various experimental conditions. 1H‐NMR spectroscopy shows that native folded protein has the tendency to polymerize under low‐salt conditions. These oligomers become covalently linked by disulfide bonds after decreasing the reduction potential, a process which is fully reversible. Cross‐linking studies with bis(sulfo‐succinimidyl)suberate and alkylation with iodoacetic acid under non‐reducing and reducing conditions document for the first time that Nef can also form homomeric structures including monomers, dimers, trimers and tetramers in cell lysates and intact cells. We found disulfide‐linked as well as non‐covalently associated oligomers. Since the N...