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PubMed1984

Diffusion-collision model for the folding kinetics of the lambda-repressor operator-binding domain.

The operator-binding domain of the lambda-repressor contains five alpha-helices and an extended N-terminal arm in the crystal structure determined by Pabo and Lewis reported in Nature 298, 443, 1982 (1). The four helices form a "box" enclosing a hydrophobic core with the fifth helix interacting with the equivalent helix in a dimer. With a small number of well-defined secondary structure elements (microdomains), the repressor is well suited for an analysis of its folding pathways and kinetics by use of the diffusion-collision model. In this paper, the basic elements of the model appropriate to a several microdomain protein are formulated and applied to a set of folding pathways consistent with the crystal structure of the operator-binding domain. The overall kinetics, as well as the time-dependence of intermediate states are determined as a function of the microdomain stability parameter.

Binding Sites↗

PubMedDate not supplied

Computational studies of the early intermediates of the bacteriorhodopsin photocycle.

Starting from a refined model of bacteriorhodopsin's ground state, alternative models of the K and L intermediates with retinal in either 13-cis or 13-14-dicis configuration have been generated by molecular dynamics simulations. All models have been submitted to electrostatic calculations in order to determine the pK1/2 values of particular residues of interest in the active site. Our pK1/2 calculations for the refined ground state can reestablish our former results, this time without adjusting the intrinsic pK of the Schiff base. For the K intermediate the electrostatic calculations show no significant change in the pK1/2 values compared to the ground state for most of the titrating groups in the active site. For the L intermediate where retinal possesses a 13-cis configuration, we found that electrostatic factors decrease the pK1/2 value of the Schiff base by 4-5 pK-units compared to the ground state. The calculations suggest that changes of the electrostatic environment via a pure 13-cis model are sufficient to produce a pK reduction of the Schiff base that will promote subsequent proton transfer steps.

Amino Acid Sequence↗