2.3 Å X-ray Structure of the Heme-Bound GAF Domain of Sensory Histidine Kinase DosT of Mycobacterium tuberculosis

详细信息    查看全文

• 作者：Larissa M. Podust ; Alexandra Ioanoviciu ; Paul R. Ortiz de Montellano
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：November 25, 2008
• 年：2008
• 卷：47
• 期：47
• 页码：12523-12531
• 全文大小：514K
• 年卷期：v.47,no.47(November 25, 2008)
• ISSN：1520-4995

文摘

Mycobacterium tuberculosis responds to changes in environmental conditions through a two-component signaling system that detects reduced O₂ tension and NO and CO exposures via the heme-binding GAF domains of two sensory histidine kinases, DosT and DevS, and the transcriptional regulator DosR. We report the first X-ray structure of the DosT heme-bound GAF domain (GAF_DosT) in both oxy and deoxy forms determined to a resolution of 2.3 Å. In GAF_DosT, heme binds in an orientation orthogonal to that in the PAS domains via a highly conserved motif, including invariant H147 as a proximal heme axial ligand. On the distal side, invariant Y169 forms stacking interactions with the heme with its long axis parallel and the plane of the ring orthogonal to the heme plane. In one of the two protein monomers in an asymmetric unit, O₂ binds as a second axial ligand to the heme iron and is stabilized via a H-bond to the OH group of Y169. The structure reveals two small tunnel-connected cavities and a pore on the protein surface that suggest a potential route for the access of O₂ to the sensing pocket. The limited conformational differences observed between differently heme iron-ligated GAF_DosT monomers in the asymmetric unit may result from crystal lattice limitations since atmospheric oxygen binding likely occurs in the crystal as a result of X-ray-induced Fe³⁺ photoreduction during diffraction data collection. Determination of the GAF_DosT structure sets up a framework in which to address ligand recognition, discrimination, and signal propagation schemes in the heme-based GAF domains of biological sensors.