Related Experiment Video
Updated: Jul 8, 2026
Metal-Limited Growth of Neisseria gonorrhoeae for Characterization of Metal-Responsive Genes and Metal Acquisition from Host Ligands
Published on: March 4, 2020
Ferrous Campylobacter jejuni truncated hemoglobin P displays an extremely high reactivity for cyanide - a comparative
Alessandro Bolli1, Chiara Ciaccio, Massimo Coletta
1Dipartimento di Biologia, Università Roma Tre, Italy.
Insights
Campylobacter jejuni
Area of Science:
- Biochemistry
- Microbiology
- Protein Science
Background:
- Campylobacter jejuni possesses two hemoglobins: Cgb and Ctb (truncated Hb group III, Cj-trHbP).
- Cgb is linked to nitrosative stress protection, while Cj-trHbP is hypothesized to be involved in O(2) chemistry.
- Understanding heme protein function in bacteria is crucial for novel therapeutic strategies.
Purpose of the Study:
- To investigate the kinetics and thermodynamics of cyanide binding to ferric (Cj-trHbP(III)) and ferrous (Cj-trHbP(II)) forms of C. jejuni truncated hemoglobin.
- To compare these binding properties with related heme proteins, including those from Mycobacterium tuberculosis.
Main Methods:
- Kinetic and thermodynamic analyses of cyanide binding to purified Cj-trHbP(III) and Cj-trHbP(II).
- Measurement of association and dissociation rate constants for cyanide binding.
- Comparative analysis with existing data for other globin and heme proteins.
Main Results:
- Cj-trHbP(II) exhibits an exceptionally high affinity for cyanide (K = 1.2 x 10(-6) M), primarily due to the highest recorded cyanide-binding association rate constant for a ferrous Hb (k(on) = 3.3 x 10(3) M(-1).s(-1)).
- Cj-trHbP(III) also shows high cyanide affinity (L = 5.8 x 10(-9) M) with a rate-limiting step in cyanide association kinetics.
- Cyanide dissociation rates from both Cj-trHbP forms are comparable to those of (in)vertebrate globins.
Conclusions:
- The remarkable cyanide affinity of Cj-trHbP(II) suggests a potential role in cyanide detoxification within Campylobacter jejuni.
- These findings provide insights into the functional diversity of bacterial hemoglobins.
- Further research may elucidate the physiological relevance of this detoxification mechanism.
Abstract:
Campylobacter jejuni hosts two hemoglobins (Hbs). The Camplylobacter jejuni single-domain Hb (called Cgb) is homologous to the globin domain of flavohemoglobin, and it has been proposed to protect the bacterium against nitrosative stress. The second Hb is called Ctb (hereafter Cj-trHbP), belongs to truncated Hb group III, and has been hypothesized to be involved in O(2) chemistry. Here, the kinetics and thermodynamics of cyanide binding to ferric and ferrous Cj-trHbP [Cj-trHbP(III) and Cj-trHbP(II), respectively] are reported and analyzed in parallel with those of related heme proteins, with particular reference to those from Mycobacterium tuberculosis. The affinity of cyanide for Cj-trHbP(II) is higher than that reported for any known (in)vertebrate globin by more than three orders of magnitude (K = 1.2 x 10(-6) m). This can be fully attributed to the highest (ever observed for a ferrous Hb) cyanide-binding association rate constant (k(on) = 3.3 x 10(3) m(-1).s(-1)), even though the binding process displays a rate-limiting step (k(max) = 9.1 s(-1)). Cj-trHbP(III) shows a very high affinity for cyanide (L = 5.8 x 10(-9) m); however, cyanide association kinetics are independent of cyanide concentration, displaying a rate-limiting step (l(max) = 2.0 x 10(-3) s(-1)). Values of the first-order rate constant for cyanide dissociation from Cj-trHbP(II)-cyanide and Cj-trHbP(III)-cyanide (k(off) =5.0 x 10(-3) s(-1) and l(off) > or = 1 x 10(-4) s(-1), respectively) are similar to those reported for (in)vertebrate globins. The very high affinity of cyanide for Cj-trHbP(II), reminiscent of that of horseradish peroxidase(II), suggests that this globin may participate in cyanide detoxification.
