  Using coarse-grained molecular dynamics simulations, we analyze mechanically
induced dissociation and unfolding of the protein complex CD48-2B4. This
heterodimer is an indispensable component of the immunological system: 2B4 is a
receptor on natural killer cells whereas CD48 is expressed on surfaces of
various immune cells. So far, its mechanostability has not been assessed either
experimentally or theoretically. We find that the dissociation processes
strongly depend on the direction of pulling and may take place in several
pathways. Interestingly, the CD48-2B4 interface can be divided into three
distinct patches that act as units when resisting the pulling forces. At
experimentally accessible pulling speeds, the characteristic mechanostability
forces are in the range between 100 and 200 pN, depending on the pulling
direction. These characteristic forces need not be associated with tensile
forces involved in the act of separation of the complex because prior
shear-involving unraveling within individual proteins may give rise to a higher
force peak.
