Ap. Wiles et al., NMR-STUDIES OF A VIRAL PROTEIN THAT MIMICS THE REGULATORS OF COMPLEMENT ACTIVATION, Journal of Molecular Biology, 272(2), 1997, pp. 253-265
Vaccinia virus complement control protein (VCP) is a 243-residue prote
in that is similar in sequence to the regulators of complement activat
ion; its role is to defend the virus against attack by the host comple
ment system. A fragment of this protein spanning the two complement pr
otein (CP)modules (residues 126 to 243) which make up the C-terminal h
alf of VCP has been expressed in Pichia pastoris. A N-15-labelled samp
le was purified for the purposes of structure determination and measur
ements of dynamics in solution using NMR. Structures were calculated o
n the basis of 1767 NMR-derived distance and angle restraints, with a
longer than normal high-temperature simulated annealing (SA) protocol
which improved convergence. The viral CP-modules are structurally very
similar to the 15th and 16th CP-modules of human factor H (fH; averag
e r.m.s.d., for invariant Trp and Cys, four pair-wise comparisons, = 1
.2 Angstrom) but less similar to the fifth CP-module of DT (average r.
m.s.d. = 2.2 Angstrom). in the VCP fragment, the orientation of one mo
dule with respect to the other is clearly defined by the experimental
data, and T-1 measurements are consistent with only limited flexibilit
y at the module-module interface. The r.m.s.d. over all of the 118 res
idues (backbone atoms) is 0.73 Angstrom. The intermodular orientation
is better defined than, and significantly different from, that observe
d in a CP-module pair from fH (re-calculated using the extended SA pro
tocol). Ln VCP the long axis of the second module is tilted by 59(+/-4
)degrees with respect to the first module (50(+/-13)degrees in the fH
pair), and twisted with respect to the first module by 22(+/-6)degrees
(223(+/-17)degrees in DI). The differences between the human and vira
l proteins may be rationalised in terms of the lack of hydrogen-bond s
tabilised secondary structure in the N-terminal portion of DI module 1
6, and the number and type of amino acid side-chains which make up the
interface. A similar intermodular interface may be predicted between
the third and fourth module of human C4 binding protein and, probably,
between the third and fourth modules of the guinea pig acrosomal matr
ix protein 67; but the formulation of general rules for predicting the
structure of interfaces between CP-modules awaits further experimenta
l data. (C) 1997 Academic Press Limited.