II. Conformational transition for entire GroEL heptamer.
The color code is the same as in the single subunit transition. The view
is looking down from the top of the heptamer. The hydrophobic residue cluster on
the apical domain that is responsible for the binding of both GroES and unfolded
polypeptide is shown in a white space-filling model to make it easier to see the
reorientation of the apical domains during the transition.
heptameric ring transition was generated by taking each frame of the single
subunit transition (shown in Movie I
) and by
repeating the equatorial domain seven times based on the 7-fold symmetry
starting with the closed x-ray structure. Thus, the relative starting positions
of the subunits are exactly those in the GroEL ring.
between each pair of adjacent apical domains maintains a tight and smooth
contact during the entire fully-concerted transition, in spite of the large
relative motion of the apical domains. There are no steric clashes along the
path. Given the nonspherical shape of the apical domain, such a result
demonstrates that the transition path determined for the single subunit
satisfies the geometric constraints of the GroEL heptameric ring. It suggests
that GroEL has evolved so that the motion of the complex is a collective
manifestation of the lowest-energy path of the individual subunit.
striking analogue for the concerted GroES-induced opening motion is the
metal-steamer basket used in cooking. The steamer basket can be opened
easily if, and only if, the symmetry is maintained; i.e., the motion of
the metal leaves (subunits) has to be concerted.
Note: The movie is
shown in loop. The starting point is the ring closed form, i.e., the
white hydrophobic ring has the smallest radius.
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