Book of Abstracts: Albany 2003
June 17-21 2003
Molecular Dynamics Simulation of Anthrax Edema Factor:Calmodulin Complexes with Mutations in the Edema Factor "Switch A" Region
Bacillus anthracis, a spore-forming infectious bacterium, produces an exotoxin (1-3), called the edema factor (EF), that functions in part by disrupting internal signalling pathways. When complexed with host cell calmodulin (CaM), EF becomes an active adenylyl cyclase, producing the internal signal substance cyclic-AMP in an uncontrolled fashion (4-9). Recently, the crystal structures for uncomplexed EF and EF:CaM complexes in the presence and absence of a substrate analog (3'-deoxy-ATP), were reported (9). EF mutational studies have implicated a number of residues important in CaM binding and/or in the generation of the adenylyl cyclase active site, formed by the movements of the EF switch A, B and C regions upon CaM binding (9).
Here we report on the results of molecular dynamics (MD) simulations on two EF:CaM complexes, one containing wild-type EF and the other containing EF in which a cluster of residues in the switch A region (L523, K525, Q526 and V529) have been mutated to alanine. The switch A mutations cause a large increase in the flexibility of the switch C region, as clearly revealed by the mean-square-displacement, MSD, traces shown in the figure below. (The switch C MSD profiles in the wild-type MD run, shown on the left, and in the Ala mutant MD run, shown on the right, are indicated by the arrows.) The switch A mutations also result in the rupture of a number of EF-CaM hydrogen-bonding interactions and an expansion of the carboxyl-terminal domain of CaM. The results indicate the importance of the mutated switch A residues in maintaining a compact EF:CaM complex that appears to be a prerequisite for the generation of a fully-functional adenylyl cyclase active site.
Gustaf H. Carlson School of Chemistry and Biochemistry