A subunit runs from   101 to 387
C subunit runs from    67 to 387
Its truncated.

The following matrix rotates C subunit so that its P domain (104-268)
superposes with that of A subunit :

Number of Selected Atoms:  165
    [ -0.4696   0.8826  -0.0236 ]        [  -20.4604 ]
R = [ -0.8807  -0.4702  -0.0581 ]    T = [   46.8588 ]
    [ -0.0624  -0.0065   0.9980 ]        [    0.2114 ]

residues 266-271 seem to do most of the moving. 

conformation 1: 2tbv-A.pdb 
conformation 2: 2tbv-C.pdb

The hinge in TBV is between residues 266 and 272 (at most 12
torsions).

   PRO 266  E  -87  139 22      E  -69  126 22      18   -13      0.8002  *
   GLN 267  R -136 -111 333     E -116  170 333     20    79      1.2410  *
   PRO 268  E  -98  131 22      E  -45  132 22      53     1      2.0779  *
   THR 269  E  -34  135 2       E  -74  118 2      -40   -17      2.1128  *
   ASN 270  R  -68  -77 11      E  -64  145 11       4   138      1.6994  *
   THR 271  E -177   57 2       E  -82  151 2       95    94      1.9718  *
   LEU 272  R  -28   -1 21      E -109   16 13     -81    17      4.0165  *

The 5 most "important" flexible torsions appear to be:

psi-267, phi-268, phi-269, psi-270, and phi-271.

Note that changes in psi(i) and phi(i+1) can cancel to some degree, so
the changes in psi-271, phi-272, and psi-266, and phi-267 may not be
that important.