Investigations of Low-Frequency Vibrational Dynamics and Ligand Binding Kinetics of Cystathionine β-Synthase

Vibrational coherence spectroscopy is used to study the low frequency dynamics of the truncated dimer of human cystathionine beta-synthase (CBS). CBS is it pyridoxal-5'-phosphate-dependent heme enzyme with cysteine and histidine axial ligands that catalyzes the condensation of serine and homocysteine to form cystathionine. A strong correlation between the detuned coherence spectrum (which probes higher frequencies) and the Raman spectrum is demonstrated, and a rich pattern of modes below 200 cm(-1) is revealed. Normal coordinate structural decomposition (NSD) of the ferric CBS crystal structure predicts the enhancement of normal modes with significant heme doming, ruffling, and saddling content, and they are observed in the coherence spectra near similar to 40, similar to 60, and similar to 90 cm(-1). When pH is varied, the relative intensities and frequencies of the low frequency heme modes indicate the presence of it unique protein-induced heme structural perturbation near pH 7 that differs from what is observed at higher or lower pH. For ferric CBS, we observe a new mode near similar to 25 cm(-1), possibly involving the response of the protein, which exhibits a phase jump of similar to pi for excitation on the blue and red side of the Soret hand maximum. The low frequency vibrational coherence spectrum of ferrous CBS is also presented, along with Our efforts to probe its NO-bound complex. The CO geminate rebinding kinetics of CBS are similar to the CO-bound form of the gene activator protein CooA, but with the appearance of a significant additional kinetic inhomogeneity. Analysis of this inhomogeneity suggests that it arises from the two Subunits of CBS and leads to it factor of similar to 20 for the ratio of the average CO geminate rebinding rates of the two subunits.