Shell-forming chains, conformations

Study of Shell-Forming Chain Conformations by Nonradiative... 

However, it can be rationalized when we postulate a rather specific conformational behavior of An-tagged shell-forming chains, which is depicted in Fig. 16. 

The model assumes the coexistence of two distinctly different conformations created by identical shell-forming chains in each micelle under equilibrium... 

In our computer studies of the conformational behavior of the shell-forming chains, we used MC simulations [91, 95] on a simple cubic lattice and studied the shell behavior of a single micelle only. Because we modeled the behavior of shells of kinetically frozen micelles, we simulated a spherical polymer brush tethered to the surface of a hydrophobic spherical core. The association number was taken from the experiment. The size of the core, lattice constant (i.e., the size of the lattice Kuhn segment ) and the effective chain length were recalculated from experimental values on the basis of the coarse graining parameterization [95]. 

In summary, the computer simulation of micelles with shells formed by an annealed PE is a combination of MC with the self-consistent field treatment of electrostatic forces. However, it goes beyond the mean-field approximation. It is also evident from simulation snapshots (see below) that the a priori assumption of the spherical symmetry of the electrostatic field (which is an inherent feature of studied micelles) does not impose a strong constraint on instantaneous chain conformations. 

The asymmetric unit contains one copy each of the subunits VPl, VP2, VP3, and VP4. VP4 is buried inside the shell and does not reach the surface. The arrangement of VPl, VP2, and VP3 on the surface of the capsid is shown in Figure 16.12a. These three different polypeptide chains build up the virus shell in a way that is analogous to that of the three different conformations A, C, and B of the same polypeptide chain in tomato bushy stunt virus. The viral coat assembles from 12 compact aggregates, or pen tamers, which contain five of each of the coat proteins. The contours of the outward-facing surfaces of the subunits give to each pentamer the shape of a molecular mountain the VPl subunits, which correspond to the A subunits in T = 3 plant viruses, cluster at the peak of the mountain VP2 and VP3 alternate around the foot and VP4 provides the foundation. The amino termini of the five VP3 subunits of the pentamer intertwine around the fivefold axis in the interior of the virion to form a p stmcture that stabilizes the pentamer and in addition interacts with VP4. 

In conclusion, it was found that complexes of poly(ethylene oxide)-h-poly(L-lysine) with retinoic acid with short poly(L-lysine) segments of 18 and 30 monomers form core shell micelles. The cores of the micelles contain a lamellar smectic A-like structure, formed by a poly(L-lysine) retinoate complex, which is surrounded by a corona of poly(ethylene oxide). Although the poly(L-lysine) chains are relatively short, they adopt an a-helical conformation to a pH as low as 9. This effective stabilization of the a-helix structure seems to be due to the formation of a protective surrounding coat of retinoate and a shell of poly(ethylene oxide). 

---