Association with molten globule

Perhaps one of the most intriguing questions of triplex function is the role of Vp23. Before its association with Vpl9C, the protein exists as a partially folded molten globule (Kirkitadze et at, 1998). And its structural variability in the 8.5-A image reconstruction of the B capsid is truly noteworthy (Zhou et at, 2000). Presumably the alternate structures of the protein in the B capsid and presumed transient structures in the procapsid are influenced by its local environment, as has been observed with 0X174 external scaffolding protein (Dokland et at, 1997, 1999). 

If the peptide aggregate is envisioned as a molten globule, one plausible mechanism (Marshall, unpublished Figure 19) for gating of a pore formed by a helical bundle embedded in the membrane is a simple reorientation of helices. a-Helices have orientations of side chains that favor nonparallel association with an angle of approximately 25° between helix axes to pack optimally (see discussion and references cited in Chou et al. (296)) as seen in the transmembrane helices of the photosynthetic reaction center (252) and of bacteriorhodopsin (297). The surface tension of the membrane tends to minimize the volume of the helical bundle. The gating potential could simply be sufficient to force the helical elements to align with the potential field with a concommitant separation of helices due to the increased steric interaction... 

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