Electrostatic effects in a large enzyme complex: subunit interactions and electrostatic potential field of the icosahedral beta 60 capsid of heavy riboflavin synthase

Proteins
A Karshikov, R Ladenstein

Abstract

The role of the electrostatic interactions in the stability of the icosahedral beta 60 capsid of heavy riboflavin synthase from Bacillus subtilis has been investigated using an approach based on the theory of Kirkwood and Tanford. The pH dependence of the electrostatic subunit interactions agrees well with experimental data. The electrostatic subunit interaction energy has a pronounced minimum at pH 8.2 for both the ligated and ligand-free capsid. The latter is characterized by a reduction of the magnitude and the pH range of the electrostatic attraction. It is found that only 8 charged groups, which form one cluster and two ion pairs, provide a significant contribution to the capsid stability. The analysis has shown that the aggregation/disaggregation equilibrium seems to be regulated by electrostatic interactions between beta-subunits forming dimers, which connect the relatively stable pentamers in the beta-60 capsid. The release of the ligand causes a reduction of the electrostatic attraction of the dimers, which may induce disaggregation of the capsid. The electrostatic potential field due to the titratable groups and alpha-helix macrodipoles has been calculated on the basis of the Coulomb relation. Two different values of ...Continue Reading

References

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