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IcmQ in the Type 4b secretion system contains an NAD+ binding domain

Jeremiah D Farelli1, James C Gumbart, Ildikó V Akey

  • 1Department of Physiology and Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118-2526, USA.

Structure (London, England : 1993)
|July 16, 2013
PubMed

Insights

The study reveals the structure of the IcmR-IcmQ complex, crucial for Legionella bacterial growth. This complex binds NAD(+) and membranes, potentially modifying Type 4b secretion system proteins.

Area of Science:

  • Microbiology
  • Structural Biology
  • Bacterial Pathogenesis

Background:

  • Legionella pneumophila requires a Type 4b secretion system (T4bSS) for intracellular growth in alveolar macrophages.
  • The IcmQ protein, associated with IcmR, plays a critical role in T4bSS function and membrane binding.

Purpose of the Study:

  • To elucidate the structural basis of the IcmR-IcmQ complex.
  • To understand the molecular mechanisms underlying IcmR-IcmQ's role in the T4bSS.

Main Methods:

  • X-ray crystallography to determine the IcmR-IcmQ complex structure.
  • Bioinformatic analysis for structural homology.
  • Molecular dynamics simulations to identify NAD(+) binding sites.
  • Site-directed mutagenesis and binding assays to validate functional predictions.

Main Results:

  • The crystal structure reveals an amphipathic four-helix bundle of IcmR and IcmQ's N-terminal domain, linked to a novel C-terminal domain (Qc).
  • The Qc domain exhibits structural homology to ADP ribosyltransferase domains and binds NAD(+) with physiological affinity.
  • An extended NAD(+) binding site on Qc was identified and validated, suggesting a functional role.

Conclusions:

  • The IcmR-IcmQ complex likely binds to bacterial membranes.
  • Upon NAD(+) binding, the complex may interact with or modify T4bSS proteins, impacting Legionella pathogenesis.

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