Knowledge of the structure of a protein can be very informative in determining its function, however, a
structure alone does not tell the whole story. In the case of large, dynamic multi-protein systems where
a coordinated network of interactions and enzymatic functions are involved, structural and biochemical
information may be gainfully combined with knowledge of dynamics . One such system is the
bacterial replisome, which consists of more than a dozen interacting proteins and is capable of rapid
DNA replication. As such, it is a good model system and a ripe target for antibiotic development. We
have focussed on an interaction that involves one of the key organisational centres of the Gram-positive
bacterial replisome, the DnaB helicase and its loading partner, DnaI, which together form a tight 6:6
complex prior to loading of the hexameric helicase onto DNA, after which DnaI dissociates . We have
separately measured the dynamics of DnaI, DnaB and their complex using elastic, quasielastic and
inelastic neutron scattering on IN6 at ILL (Grenoble, France).
These measurements have established that the molecular fl exibility and diffusive motions are
signifi cantly decreased when DnaI and DnaB are complexed, with DnaB having the greatest fl exibility
when free. Further to this, complexation results in an increase in structural rigidity with the DnaB-DnaI
complex having a signifi cantly higher effective force constant both above and below the temperature of
dynamical transition. The vibrational density of states was also extracted, revealing that the DnaI-DnaB
complex has less inelastic vibrational modes than DnaB and DnaI below the absolute value of 20 meV.
 M. Tehei, A. Frölich, F. Gabel, M. Jasnin, U. Lehnert, D. Oesterhelt, A. M. Stadler, M. Weik, K. Wood and G.
Zaccai, Faraday Discuss., 141, 117 (2009)
 K. V. Loscha, K. Jaudzems, C. Ioannou, X. C. Su, F. R. Hill, G. Otting, N. E. Dixon and E. Liepinsh, Nucleic
Acids Res., 37, 2395 (2009)