On the Stability of the Water-Soluble Chlorophyll-Binding Protein (WSCP) Studied by Molecular Dynamics Simulations.

The water-soluble chlorophyll-binding Protein (WSCP) is assumed to be not part of the photosyntetic process. Applying molecular dynamics (MD) simulations we aimed to obtain insight into the exceptional stability of WSCP. We analyzed dynamical features such as the hydrogen bond network, flexibility and force distributions. The WSCP structure contains two cysteines at the interfaces of every protein chain, which are in close contact to the cysteines of the other dimer. We tested if a connection of these cysteines between different protein chains influences the dynamical behavior to investigate any influences on the thermal stability. We find that the hydrogen bond network is very stable regardless of the presence or absence of the hypothetical disulfide bridges and/or the chlorophyll units. Furthermore, it is found that the phytyl chains of the chlorophyll units are extremely flexible, much more than what is seen in crystal structures. Nonetheless, they seem to protect a photochemically active site of the chlorophylls over the complete simulation time. Finally, we also find that a cavity in the chlorophyll-surrounding sheath exists, which may allow access for individual small molecules to the core of WSCP.