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T Bellini

Publications and source records attributed to T Bellini.

At least 37 records · Page 2Linked to original sources
PubMed1995

Activation of the Sendai virus fusion protein by receptor binding.

2,3 Dehydro-2-deoxy-N-acetyl-neuraminic acid (DNANA) competitively inhibits the neuraminidase activity of Hemagglutinin-neuraminidase (HN) from Sendai virus. The inhibition constant depends on the presence of the Fusion (F) protein, which is 30 microM in the presence of active F protein and 50 microM when the F protein is inactivated. These data correlate with previously reported evidence of interaction of the F protein with HN (Dallocchio, F., Tomasi, M., & Bellini, T. (1994) Biochem. Biophys. Res. Comm. 201, 988-993). Desialyzation of erythrocytes, by Clostridium neuraminidase, lowers the hemolytic activity of SV to < 0.1% of that observed on untreated erythrocytes. However, addition of DNANA causes a concentration-dependent increase of hemolytic activity. Both HN and the F protein are required for the activation of hemolytic activity by DNANA. The affinity constant for DNANA, calculated from the activation of hemolytic activity on desialyzed erythrocytes, is 35 microM, very close to the Ki for neuraminidase activity. These data suggest that the binding of the F protein to HN, induced by the binding to HN of a substrate or a substrate analogue, causes a conformational change which activates the F protein.

Allantois↗
PubMed1994

Inhibition of Sendai virus hemagglutinin neuraminidase by the fusion protein.

The Sendai virus envelope contains two glycoproteins: the fusion (F) protein and the hemagglutinin-neuraminidase (HN). Inactivation of F causes the loss of fusogenic activity and an increase of the neuraminidase activity of HN. After inactivation of F, HN can be inhibited by fetuin or asialofetuin, as already observed on the water-soluble, C-terminal fragment of HN (Dallocchio, F., Bellini, T., Martuscelli, G., Baiocchi, M., & Tomasi, M. (1991) Biochem. Int. 25, 663-668). Disruption of viral envelopes by detergents does not affect the neuraminidase activity of virions containing inactive F, while it causes an increase of the neuraminidase activity in native virions. Reconstitution of HN into liposomes is accompanied by a decrease of enzymatic activity, due to the random inside-outside distribution of the protein. However, the decrease of the neuraminidase activity is higher in liposomes containing both HN and F. These data suggest that F inhibits the neuraminidase activity of HN.

Animals↗
PubMed1993

Selective modification of Sendai virus hemagglutinin neuraminidase by pyridoxal 5'-phosphate: evidence for an allosteric modulation of neuraminidase activity.

Incubation of Sendai virus with pyridoxal 5'-phosphate (PLP) causes inhibition of hemolytic activity, a slight reduction of hemagglutinating activity, and an increase in neuraminidase activity. The effects on hemagglutination and neuraminidase are prevented by the presence in the incubation mixture of sialyl lactose, a substrate of hemagglutinin-neuraminidase. Incubation with PLP of the water-soluble enzymatic domain of the neuraminidase has no effect on enzymatic activity, while the allosteric inhibition (Dallocchio et al. (1991) Biochem. Int. 25, 663-668) disappears. Both virus-bound and solubilized neuraminidase are selectively modified by PLP at the lysine-553. Our data suggest that PLP inactivates a previously undetected inhibitory site on the viral neuraminidase, and that a physiological effector is present on the viral envelope.

Allosteric Regulation↗
PubMed1991

Allosteric inhibition of the water-soluble C-terminal fragment of Sendai virus neuraminidase.

Trypsin solubilized hemagglutinin-neuraminidase of Sendai virus (cHN) displays michaelian kinetics, with native fetuin as substrate, at 37 degrees C. Vmax and Km values are only marginally altered, as compared to intact viral neuraminidase. At lower temperatures, cHN follows non-michaelian kinetics, with marked substrate inhibition at 4 degrees C. With denaturated fetuin, michaelian kinetics are observed in all conditions, while asialo fetuin was an uncompetitive inhibitor of cHN, with native fetuin or sialyl lactose as substrates. These results can be explained assuming that the protein moiety of fetuin acts as an allosteric inhibitor of cHN.

Allosteric Site↗
PubMed1990

Myelin basic protein inhibits the calcium response to phytohaemagglutinin in human lymphocytes.

Myelin Basic Protein, one of the major membrane protein component of the central nervous system, was used to probe the molecular mechanism of cellular activation by phytohaemagglutinin. Pre-treatment of human lymphocytes with myelin basic protein results in a lower rising of cytosolic concentration of free calcium after stimulation with phytohaemagglutinin. This effect is dependent on myelin basic protein concentration and on the preincubation time of the protein with the cells. It is not due to a interaction between myelin basic protein and phytohaemagglutinin, but appears to be a consequence of the binding of the protein to the cell surface. The reduction of the rise of cytosolic calcium induced by phytohaemagglutinin is specific for the myelin basic protein because other proteins like albumin and protamine have no effect.

Calcium↗
PubMed1990

Effect of 17 beta-estradiol on calcium response to phytohaemagglutinin in human lymphocytes.

Pre-treatment of human lymphocytes with 17 beta-estradiol diminishes the increase in concentration of cytosolic free calcium after stimulation with phytohaemagglutinin. The effect is dependent on 17 beta-estradiol concentration and on the preincubation time. The effect is not due to an interaction between 17 beta-estradiol and phytohaemagglutinin, but appears to be a consequence of the binding of the hormone to the cell surface. The effect is specific for 17 beta-estradiol, since the alpha isomer and other steroid hormones (progesterone, testosterone, diethylstilbestrol and 5 alpha-androstan) have no effect. Since the effect of the 17 beta-estradiol can be suppressed by treatment of lymphocytes with ouabain, it appears that the effect of estradiol on the rise of cytosolic calcium induced by phytohaemagglutinin is mediated by the (Na, K)-ATPase.

Calcium↗