Barnase-barstar

Active sites of enzymes and binding sites of proteins are a general source of instability because they contain groups that are exposed to solvent in order to bind substrates and ligands and so are not paired with their normal types of partners. Stability-activity trade-off is also seen with residues in the natural polypeptide inhibitor of barnase, barstar, that has evolved to bind as rapidly as possible to barnase,70 and also in the active site of T4 lysozyme.71... 

In our simulations, we performed association studies to elucidate their role by selecting pairs of those hot spot residues that established a barnase-barstar contact in the bound complex. In these simulations, we studied what effect the side-chain conformation had on contact formation for certain hot spot residue pairs. A typical result is shown in Figure 8. Starting from the correct rotameric state for certain hot spot residue pairs with the rest of the proteins in their unbound conformations leads to improved contact formation in the initial docking phase. This effect is not observed when performing equivalent simulations with non-hot-spot interfacial residue pairs. 

The results of simulating barnase-barstar association after 100 ps of simple multiple copy MD without ensemble enriching are shown in Figure 9. Whereas contact formation in the simple multiple copy MD simulation has leveled off after the initial 100 ps, ensemble enriching with a linear scoring function is able to shift the ensemble population toward a higher number of established native contacts. Compared to the side-chain torsion dynamics... 

Interactions Analysis of the Barnase-Barstar Interface by Single Mutations and Double Mutant Cycles. 

Recognition Crystal Structural Analysis of a Barnase—Barstar Complex at 2.0-A Resolution. 

Schreiber G, Fersht AR (1995) Energetics of protein-protein interactions analysis of the barnase-barstar interface by single mutations and double mutant cycles, J Mol Biol, 248 -178 1X9... 

The AH and AG values of Fig. 11 may be compared with these data. They were derived from a relatively unsophisticated attempt to reproduce in the computer the energetics of the HyHel5-lysozyme and barnase-barstar systems, based on the atomic coordinates of the two complexes... 

In the barnase-barstar system, there is a selective pressure on the kinetics of association, the ribonuclease activity being lethal if expressed in the cell. The genes form an operon and, when both proteins are produced together in the bacterium, barnase must be either excreted or immediately inhibited by barstar. Unlike the selection for tight binding, which operates almost exclusively on residues at the interface, the selection for fast binding acts on all charged residues of the two proteins. 

Buckle, A. M., Schreiber, G., and Fersht, A. R. (1994). Protein-protein recognition Crystal structural analysis of a barnase-barstar complex at 2.0-A resolution. Biochemistry 33(30), 8878-8889. 

A. M. Buckle, G. Schreiber, and A. R. Fersht, Biochemistry, 33, 8878-8889 (1994). Protein-Protein Recognition Crystal Structural Analysis of a Barnase-Barstar Complex at 2.0-A Resolution. 

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