Dynamics of carbon monoxide binding to cystathionine βsynthase

Mrinalini Puranik, Colin L. Weeks, Dorothee Lahaye, Ömer Kabil, Shinichi Taoka, Steen Brøndsted Nielsen, John Taylor Groves, Ruma Banerjee, Thomas G. Spiro

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75 Scopus citations


Cystathionine β-synthase (CBS) condenses homocysteine, a toxic metabolite, with serine in a pyridoxal phosphate-dependent reaction. It also contains a heme cofactor to which carbon monoxide (CO) or nitric oxide can bind, resulting in enzyme inhibition. To understand the mechanism of this regulation, we have investigated the equilibria and kinetics of CO binding to the highly active catalytic core of CBS, which is dimeric. CBS exhibits strong anticooperativity in CO binding with successive association constants of 0.24 and 0.02 μM-1. Stopped flow measurements reveal slow CO association (0.0166 s-1) limited by dissociation of the endogenous ligand, Cys-52. Rebinding of CO and of Cys-52 following CO photodissociation were independently monitored via time-resolved resonance Raman spectroscopy. The Cys-52 rebinding rate, 4000 s-1, is essentially unchanged between pH7.6 and 10.5, indicating that the pKa of Cys-52 is shifted below pH7.6. This effect is attributed to the nearby Arg-266 residue, which is proposed to form a salt bridge with the dissociated Cys-52, thereby inhibiting its protonation and slowing rebinding to the Fe. This salt bridge suggests a pathway for enzyme inactivation upon CO binding, because Arg-266 is located on a helix that connects the heme and pyridoxal phosphate cofactor domains.

Original languageEnglish (US)
Pages (from-to)13433-13438
Number of pages6
JournalJournal of Biological Chemistry
Issue number19
StatePublished - May 12 2006

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Biochemistry
  • Cell Biology


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