  We consider mechanical stability of dimeric and monomeric proteins with the
cystine knot motif. A structure based dynamical model is used to demonstrate
that all dimeric and some monomeric proteins of this kind should have
considerable resistance to stretching that is significantly larger than that of
titin. The mechanisms of the large mechanostability are elucidated. In most
cases, it originates from the induced formation of one or two cystine
slipknots. Since there are four termini in a dimer, there are several ways of
selecting two of them to pull by. We show that in the cystine knot systems,
there is strong anisotropy in mechanostability and force patterns related to
the selection. We show that the thermodynamic stability of the dimers is
enhanced compared to the constituting monomers whereas machanostability is
either lower or higher.
