Mechanisms of interaction of amino acids with phospholipid bilayers during freezing

In this study we compare the ability of various amino acids to protect small unilamellar vesicles against damage during freeze/thaw. Liposomes were composed of 75% palmitoyloleoyl phosphatidylcholine and 25% phosphatidylserine. Damage to liposomes frozen in liquid nitrogen and thawed at 20 degrees C was assessed by resonance energy transfer. Cryoprotection by numerous amino acids was compared in the presence and absence of 350 mM NaCl. The majority of amino acids with hydrocarbon side chains increased membrane damage during freeze/thaw regardless of the presence of salt. However, amino acids with hydrocarbon side chains of less than three carbons long, e.g. glycine, alanine, and 2-aminobutyric acid, were cryoprotective only in the presence of salt. We suggest that NaCl selectively increases the solubility of such amino acids, allowing them to act as cryoprotectants. In contrast, amino acids with side chains containing charged amine groups were cryoprotective regardless of the presence of salt. The degree of charge on the second amine group is shown to be important for cryoprotection by these molecules. We present evidence that suggests an interaction between the positively charged, second amine group of the amino acid, and the negatively charged phospholipid headgroup.     

Long-term preservation of dried phosphofructokinase by sugars and sugar/zinc mixtures

We have demonstrated that sugars and suger/zinc mixtures can be used to preserve the activity of dried phosphofructokinase (PFK) during long-term storage over CaSO4. After 9 weeks in the presence of either 200 mM sucrose or 200 mM trehalose little loss of PFK activity was noted, with almost 60% of the original prefreeze-dry activity recovered when samples were rehydrated. Even reducing sugars protected the dried enzyme throughout the entire storage period. Of the sugars tested, 200 mM lactose provided the most stability to PFK; at the end of the dry storage, over 80% of the initial activity was recovered. With either 200 mM maltose or 400 mM glucose, about 40% of the initial activity was recovered at the end of the experiment. With all the sugars tested, the addition of 0.6 mM Zn2+ to sugar/PFK mixtures enhanced the stability of the enzyme, and no long-term adverse effects of the metal ion on enzyme activity were noted.     

SEED DORMANCY IN UNIOLA PANICULATA

Seeds of Uniola paniculata L., a sand-dune grass of the Southeast coast, showed an increasing dormancy under laboratory germination conditions that reached 98–100% six months after maturity. The embryos were viable and nondormant and the seeds absorbed water readily. Chemical treatments were only moderately effective, but leaching the seeds after cutting into the endosperm gave 100% germination. The presence of a diffusible growth inhibitor was demonstrated by this response and by tests of endosperm leachate. Temperature, particularly sand temperature above 30 C, appears to be the major factor in normal germination of the seed.     

Fasting protects against the side effects of irinotecan but preserves its anti-tumor effect in Apc15lox mutant mice

Irinotecan is a widely used topoisomerase-I-inhibitor with a very narrow therapeutic window because of its severe toxicity. In the current study we have examined the effects of fasting prior to irinotecan treatment on toxicity and anti-tumor activity. FabplCre;Apc^15lox/+ mice, which spontaneously develop intestinal tumors, of 27 weeks of age were randomized into 3-day fasted and ad libitum fed groups, followed by treatment with a flat-fixed high dose of irinotecan or vehicle. Side-effects were recorded until 11 days after the start of the experiment. Tumor size, and markers for cell-cycle activity, proliferation, angiogenesis, and senescence were measured. Fasted mice were protected against the side-effects of irinotecan treatment. Ad libitum fed mice developed visible signs of discomfort including weight loss, lower activity, ruffled coat, hunched-back posture, diarrhea, and leukopenia. Irinotecan reduced tumor size in fasted and ad libitum fed groups similarly compared to untreated controls (2.4 ± 0.67 mm and 2.4 ± 0.82 mm versus 3.0 ± 1.05 mm and 2.8 ± 1.08 mm respectively, P < 0.001). Immunohistochemical analysis showed reduced proliferation, a reduced number of vascular endothelial cells, and increased levels of senescence in tumors of both irinotecan treated groups. In conclusion, 3 days of fasting protects against the toxic side-effects of irinotecan in a clinically relevant mouse model of spontaneously developing colorectal cancer without affecting its anti-tumor activity. These results support fasting as a powerful way to improve treatment of colorectal carcinoma patients.     

Unconventional Secretion of AcbA in Dictyostelium discoideum through a Vesicular Intermediate

The acyl coenzyme A (CoA) binding protein AcbA is secreted unconventionally and processed into spore differentiation factor 2 (SDF-2), a peptide that coordinates sporulation in Dictyostelium discoideum. We report that AcbA is localized in vesicles that accumulate in the cortex of prespore cells just prior to sporulation. These vesicles are not observed after cells are stimulated to release AcbA but remain visible after stimulation in cells lacking the Golgi reassembly stacking protein (GRASP). Acyl-CoA binding is required for the inclusion of AcbA in these vesicles, and the secretion of AcbA requires N-ethylmaleimide-sensitive factor (NSF). About 1% of the total cellular AcbA can be purified within membrane-bound vesicles. The yield of vesicles decreases dramatically when purified from wild-type cells that were stimulated to release AcbA, whereas the yield from GRASP mutant cells was only modestly altered by stimulation. We suggest that these AcbA-containing vesicles are secretion intermediates and that GRASP functions at a late step leading to the docking/fusion of these vesicles at the cell surface.The acyl coenzyme A (CoA) binding protein (ACBP) has been well characterized for its role in intracellular lipid trafficking, but it also serves as the precursor of peptides that function as intercellular signals. ACBPs are involved in the transport and metabolism of long-chain acyl-CoA esters and steroid biosynthesis (15, 16, 32). In the mammalian brain ACBP is also secreted and processed to generate a diazepam binding inhibitor (DBI) peptide that regulates γ-aminobutyric acid A (GABA_A) ionotropic receptors in neurons (12). Qian and colleagues recently demonstrated the secretion of ACBP from Muller glial cells of the retina (36). In Dictyostelium discoideum the ACBP homolog AcbA is secreted and processed extracellularly into spore differentiation factor 2 (SDF-2), a 34-amino-acid peptide that is highly similar to DBI (2). However, neither ACBP nor AcbA carries a signal sequence that is necessary for entering the endoplasmic reticulum/Golgi pathway. Alternative, unconventional pathways for the secretion of proteins, including ACBPs, have been proposed over the past 20 years, involving the direct membrane transport of proteins, novel membrane trafficking, or autophagy (29, 39).In Dictyostelium, SDF-2 signaling controls the terminal cell differentiation of prespore cells into encapsulated spores during fruiting body formation. Prespore cells within the nascent sorus climb the elongating stalk in a process that requires their active motility (8). The extracellular processing of AcbA into SDF-2 by prestalk cells is thought to coordinate spore encapsulation with fruiting body morphogenesis such that immobile spores are not produced before the stalk begins to form. Approximately halfway through this process of culmination, sporulation occurs as a wave from the top to the bottom of the nascent sorus (38).An understanding of the regulation of SDF-2 signaling is now emerging. During culmination, prespore cells respond to a steroid signal by rapidly releasing GABA, which binds to the GABA_B-like receptor GrlE and stimulates a signal transduction pathway leading to the release of AcbA by prespore cells (3, 5). AcbA is processed into SDF-2 by TagC protease, which is displayed on the surface of prestalk cells in response to GABA. The 34-amino-acid peptide SDF-2 binds to the receptor histidine kinase DhkA, leading to elevated levels of intracellular cyclic AMP (cAMP), which induces spore encapsulation (2, 47). Low levels of SDF-2 also trigger the release of additional AcbA proteins, forming a positive-feedback loop (2, 6). Although only 1 to 3% of the total AcbA is secreted, the levels of SDF-2 in the sorus are far above that required to rapidly induce sporulation (5, 19).The release of AcbA is a critical step in this cascade, but the mechanism of its secretion is largely unknown. The Golgi-associated protein GRASP (Golgi reassembly stacking protein) appears to play an essential role in the process since grpA-null mutants lacking GRASP fail to produce SDF-2 (19). To further explore the role of GRASP and understand the regulation of AcbA secretion, we have determined the subcellular localization of AcbA before and after stimulating its release. Secreted AcbA appears to be localized within membrane-bound vesicles, which accumulate in the cortex of prespore cells during culmination. When AcbA secretion is stimulated by GABA or SDF-2, the cortical vesicles containing AcbA are lost from wild-type cells but remain in cells lacking GRASP. It appears that GRASP is not involved in the production or positioning of AcbA within the cortical vesicles, but it is essential for events leading to their regulated release.     

Membrane association of VP22, a herpes simplex virus type 1 tegument protein

Tegument proteins of herpes simplex virus type 1 (HSV-1) are hypothesized to contain the functional information required for the budding or envelopment process proposed to occur at cytoplasmic compartments of the host cell. One of the most abundant tegument proteins of HSV-1 is the U(L)49 gene product, VP22, a 38-kDa protein of unknown function. To study its subcellular localization, a VP22-green fluorescent protein chimera was expressed in transfected human melanoma (A7) cells. In the absence of other HSV-1 proteins, VP22 localizes to acidic compartments of the cell that may include the trans-Golgi network (TGN), suggesting that this protein is membrane associated. Membrane pelleting and membrane flotation assays confirmed that VP22 partitions with the cellular membrane fraction. Through truncation mutagenesis, we determined that the membrane association of VP22 is a property attributed to amino acids 120 to 225 of this 301-amino-acid protein. The above results demonstrate that VP22 contains specific information required for targeting to membranes of acidic compartments of the cell which may be derived from the TGN, suggesting a potential role for VP22 during tegumentation and/or final envelopment.