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Biomedical subjects

A M Haywood

Publications and source records attributed to A M Haywood.

At least 19 recordsLinked to original sources
PubMed1986

Ficoll and dextran enhance adhesion of Sendai virus to liposomes containing receptor (ganglioside GD1a).

Previous work has shown that high-speed centrifugation (300,000 g) of Sendai virus and liposomes in 40% (w/v) sucrose layered under a discontinuous sucrose gradient removes Sendai virus bound to liposomes containing the ganglioside GD1a, a Sendai virus receptor. Centrifugation also removes virus bound to liposomes containing other negatively charged lipids. This work shows that centrifugation of virus through a discontinuous ficoll gradient does not remove virus bound to liposomes containing GD1a but does remove virus from liposomes containing various other negatively charged lipids including the ganglioside GM1, which is not a Sendai virus receptor. The amount of virus that adheres to liposomes increases with increasing content of GD1a in the liposomes. The adhesion of virus to receptor-containing liposomes during centrifugation through a ficoll gradient results from the presence of ficoll and increases with increasing ficoll concentration. Virus also adheres to receptor-containing liposomes during centrifugation in the presence of dextran. These data indicate that caution should be used in interpreting associations demonstrated by centrifugation through dextran and ficoll gradients. They also indicate that binding of virus by ganglioside receptors can be modulated by carbohydrate polymers, which are thought not to have any specific interaction with either viruses or gangliosides.

Animals↗
PubMed1986

Time and temperature dependence of influenza virus membrane fusion at neutral pH.

The time course and temperature requirements for fusion of influenza virus membranes with liposomes at pH 7.5 were found to be consistent with the requirements for cell entry. At 37 degrees C, fusion was most rapid during the first 5 min and then continued more slowly up to at least 1 h. The amount of fusion increased semilogarithmically with increasing temperature up to 50 degrees C.

Hemagglutinin Glycoproteins, Influenza Virus↗
PubMed1985

Fusion of influenza virus membranes with liposomes at pH 7.5.

Influenza virus X-31 (H3N2) membranes fuse with liposomes containing ganglioside GD1a at pH 7.5. Fusion was demonstrated by electron microscopy and also can be measured by counting the labeled virus proteins incorporated into liposomes after bound virus has been removed. Liposomes composed of lipids that have no net charge behave as reported by other investigators and do not fuse with influenza X-31 membranes at neutral pH, but they do fuse at low pH. Therefore, the liposomal composition is a factor in whether liposomes fuse with influenza virus membranes at neutral pH, probably by determining whether binding occurs. The liposomal composition necessary for fusion at neutral pH needs to be individualized for each influenza subtype. To establish that a virus requires low pH for membrane fusion, it is first necessary to establish that fusion does not occur at neutral pH under conditions where adequate binding occurs.

Animals↗
PubMed1984

Effect of lipid composition upon fusion of liposomes with Sendai virus membranes.

How the lipid composition of liposomes determines their ability to fuse with Sendai virus membranes was tested. Liposomes were made of compositions designed to test postulated mechanisms of membrane fusion that require specific lipids. Fusion does not require the presence of lipids that can form micelles such as gangliosides or lipids that can undergo lamellar to hexagonal phase transitions such as phosphatidylethanolamine (PE), nor is a phosphatidylinositol (PI) to phosphatidic acid (PA) conversion required, since fusion occurs with liposomes containing phosphatidylcholine (PC) and any one of many different negatively charged lipids such as gangliosides, phosphatidylserine (PS), phosphatidylglycerol, dicetyl phosphate, PI, or PA. A negatively charged lipid is required since fusion does not occur with neutral liposomes containing PC and a neutral lipid such as globoside, sphingomyelin, or PE. Fusion of Sendai virus membranes with liposomes that contain PC and PS does not require Ca2+, so an anhydrous complex with Ca2+ or a Ca2+-induced lateral phase separation is not required although the possibility remains that viral binding causes a lateral phase separation. Sendai virus membranes can fuse with liposomes containing only PS, so a packing defect between domains of two different lipids is not required. The concentration of PS required for fusion to occur is approximately 10-fold higher than that required for ganglioside GD1a, which has been shown to act as a Sendai virus receptor. When cholesterol is added as a third lipid to liposomes containing PC and GD1a, the amount of fusion decreases if the GD1a concentration is low.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗
PubMed1982

Sendai virus membrane fusion: time course and effect of temperature, pH, calcium, and receptor concentration.

The conditions that optimize Sendai virus membrane fusion with liposomes have been studied. No fusion occurs in the absence of ganglioside receptors. Maximum fusion occurs when the molar ratio of ganglioside GD1a to phospholipid is 0.02 or greater. The amount of fusion at 37 degrees C increases with time up to at least 6.5 h. The rate of fusion increases from the lowest temperature tested, 10 degrees C, to 40 degrees C. Above 43 degrees C the amount of fusion decreases because of thermal inactivation of the viral proteins. There is a broad pH maximum between pH 7.5 and pH 9.0. At both ends of the pH range the amount of fusion increases and exceeds that found in the physiologic pH range. Neither ethylenediaminetetraacetic acid nor Ca2+ changes the amount of membrane fusion. The optimal conditions for membrane fusion of Sendai virus membranes with liposomes are the same as the optimal conditions for fusion with host cells and with red blood cells. Since the liposomes contain no proteins, the optimal conditions for Sendai virus membrane fusion must be determined by the viral proteins and be mostly independent of the nature or presence of the host proteins.

Animals↗
PubMed1981

Initiation of fusion and disassembly of Sendai virus membranes into liposomes.

Sendai virus penetration into liposomes consists of two steps which are fusion of the viral and liposomal membranes and viral disassembly. Penetration can occur in less than one minute. The virus first causes a liposome to envelop it and then fuses with the leading edge of the developing vacuole. Viral disassembly does not follow immediately but requires release of virus-receptor binding and probably also requires changes in the association between viral proteins.

Liposomes↗
PubMed1975

'Phagocytosis' of sendai virus by model membranes.

Sendai viruses were attached to liposomes (vesicular model membranes) at 0 to 4 degrees C, and were then incubated at 37 degrees C. Liposomes made of phosphatidylcholine, cholesterol and gangliosides enveloped the viruses at 37 degrees C to give a picture that resembles the ingestion step of phagocytosis. Virus particles were enveloped only by liposomes that contained gangliosides which serve as Sendai virus receptors.

Adsorption↗
PubMed1973

Two classes of membrane binding of replicative RNA of bacteriophage MS2.

Escherichia coli membranes were isolated in the presence of 6 mM Mg(++). They were washed with buffer containing no Mg(++) to yield a fraction containing material bound only in the presence of divalent cations, "membrane eluate," and that bound in the absence of divalent cations, "membrane." When E. coli infected with bacteriophage MS2 are labeled with [(14)C]uracil, all MS2 replicative RNA, i.e., the RNA species containing MS2 complementary RNA, is in the membrane eluate and membrane. The amount of [(14)C]uracil in replicative RNA found in the membrane eluate increases with time of labeling, whereas that in the replicative RNA in the membrane reaches a plateau in 1-2 min. This finding is consistent with a precursor-product relationship. Most of the label entering single-stranded viral RNA comes from the replicative RNA in the membrane eluate. This result suggests that polymerase components or factors required for complementary-strand synthesis are bound to membrane even in the absence of divalent cations and that the polymerase is no longer bound to these factors when it is making the bulk of the progeny single-stranded RNA.

Binding Sites↗
PubMed1973

Thermal inactivation of Newcastle disease virus. I. Coupled inactivation rates of hemagglutinating and neuraminidase activities.

The thermal stability of Newcastle disease virus has been characterized in terms of the rate constants for inactivation of hemagglutinating activity (HA), neuraminidase activity (NA), and infectivity. Inactivation of HA results in the concomitant loss of NA. Infectivity, however, is much more thermolabile. Disintegration of the virus particle is not responsible for the identical rate constants for inactivation of HA and NA, nor is their parallel inactivation uncoupled in envelope fragments produced by pretreating the virus with phospholipase-C. The data indicate that a common envelope factor(s) can influence the thermal stability of both activities.

Animals↗