Biomedical subjects

B Michels

Publications and source records attributed to B Michels.

10 recordsLinked to original sources

PubMed1992

Scanning calorimetric studies of the stability of tobacco mosaic virus and aggregates of its coat protein.

The thermal denaturation of the common strain of a rod-shaped plant virus, tobacco mosaic virus, has been investigated by differential scanning calorimetry, and compared to that of various aggregation states of its coat protein and to that of three other TMV strains. The state of the virions was monitored by electron microscopy and analytical ultracentrifugation. The observed endotherms could be analysed in terms of a step-wise dissociation of the virions. The transition temperatures of the three successive structural changes increased with decreasing pH, from pH = 8.0 to pH = 5.0, although the corresponding enthalpy changes did not vary appreciably with pH. TMV-HR showed a stronger pH dependence of the transition temperatures than the other strains, probably reflecting the importance of the changes in affecting the charged amino acids of its coat protein. The first step of the dissociation, which correlates with the breaking up of the virions into three or four shorter rods, implies a conformational change of the particle that may be related to the first step of the in situ decapsidation of TMV.

Biophysical Phenomena↗

PubMed1989

Enhanced fluctuations in small phospholipid bilayer vesicles containing cholesterol.

Ultrasonic and calorimetric studies of small homogeneously-sized DMPC unilamellar vesicles showed two thermal transitions at temperatures Tc1 and Tc2 (Tc2 greater than or equal to Tc1); Tc2 is close to the phase transition temperature, Tc, of large vesicles. The process at Tc2 is not a fusion of vesicles and is interpreted as characterizing an order-disorder transition essentially similar to that of large vesicles. The temperatures Tc1 and Tc2 become increasingly similar as the cholesterol content is increased, while the clusters at Tc2 (congruent to 85 lipid molecules in pure DMPC) increase in size up to approximately 180 lipid molecules at 12 mol% cholesterol. Incorporation of cholesterol thus brings about enhanced fluctuations in this model system of a membrane.

Calorimetry↗

PubMed1985

Ultrasonic absorption in tobacco mosaic virus and its protein aggregates.

The structural fluctuations specific to self-assembled biological systems have been investigated further with ultrasonic techniques by using two strains of tobacco mosaic virus (TMV), as well as the helical aggregate of the common strain protein and subassemblies of it. We confirmed our earlier conclusion that protein assemblies exhibit specific structural fluctuations detected in ultrasonic experiments. As in spherical viruses, the fluctuations exhibited by the protein aggregates having a quaternary structure similar to that of the virion were modified in the virus by interaction with the RNA strand. It is unlikely that the origin for the observed effect is due either to: (1) the difference in local mobility of the segment 89 to 113 of the polypeptide chain in TMV and in the helical aggregate on the one hand, and in smaller aggregates, on the other hand; or (2) a local fluctuation associated with proton transfer reactions or ion-pair interactions. The most remarkable feature in the TMV system is the fact that the two-ring disk showed no excess of ultrasonic absorption with respect to the A-protein oligomer, while a large increase of ultrasonic absorption was observed in the rod-like aggregate that had undergone the disk-helix transition.

Hydrogen-Ion Concentration↗

PubMed1983

Ultrasonic absorption evidence for structural fluctuations in frog virus 3 and its subparticles.

The structural fluctuations specific to self-assemblies of biological molecules have been investigated further with ultrasonic techniques by using frog virus 3 (FV3). We compared the ultrasonic properties of complete FV3 virions and of several subparticles that may be obtained from this DNA virus: (i) the central nucleoprotein core versus its component DNA and proteins in a dissociated state; (ii) the core versus the capsidless subparticle, consisting of the core surrounded by the lipid membrane; and (iii) the complete virus versus the capsidless subparticle. The ultrasonic absorption by the core particle was quite large compared with the absorption by other nucleoprotein assemblies, suggesting that the core contains some organized structure. Both the core and the complete virus absorbed ultrasound more than did the capsidless subparticle. The difference spectrum for the virion relative to the capsidless subparticle may represent a single relaxation and is analyzed, by using a recent model, in terms of volume fluctuations due to radial movements in the virion. These fluctuations are much smaller than can be detected in virus crystals with present-day x-ray techniques.

Animals↗

PubMed1979

Ultrasonic absorption evidence of structural fluctuations in viral capsids.

When the coat protein of the small icosahedral virus, brome mosaic virus, reassembles into capsids, the ultrasonic absorption of the solution greatly increases. Submitting the solution to an ultrasonic field thus appears to reveal spontaneous molecular motions within a protein assembly. Confirmatory evidence of a dynamics of a protein shell comes from measurements on brome mosaic virus at various degrees of swelling and on tomato bushy stunt virus treated with the crosslinking agent glutaraldehyde. The detected fluctuations may be related either with cooperative deformational motion in the capsid or with more localized structural changes. Such structural changes may help liberate the RNA at an early stage of viral infection.

Mosaic Viruses↗

PubMed1974