Characterization of Staphylococcus aureus EssB, an integral membrane component of the Type VII secretion system: atomic resolution crystal structure of the cytoplasmic segment

DOI: 10.1042/BJ20121209

Authors: Martin Zoltner (University of Dundee) , Paul Fyfe (University of Dundee) , Tracy Palmer (University of Dundee) , William Hunter (University of Dundee)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Biochemical Journal , VOL 449 , PAGES 469 - 477

State: Published (Approved)
Published: January 2013

Abstract: The Type VII protein translocation/secretion system, unique to Gram-positive bacteria, is a key virulence determinant in Staphylococcus aureus. We aim to characterize the architecture of this secretion machinery and now describe the present study of S. aureus EssB, a 52 kDa bitopic membrane protein essential for secretion of the ESAT-6 (early secretory antigenic target of 6 kDa) family of proteins, the prototypic substrate of Type VII secretion. Full-length EssB was heterologously expressed in Escherichia coli, solubilized from the bacterial membrane, purified to homogeneity and shown to be dimeric. A C-terminal truncation, EssB?C, and two soluble fragments termed EssB-N and EssB-C, predicted to occur on either side of the cytoplasmic membrane, have been successfully purified in a recombinant form, characterized and, together with the full-length protein, used in crystallization trials. EssB-N, the 25 kDa N-terminal cytoplasmic fragment, gave well-ordered crystals and we report the structure, determined by SAD (single-wavelength anomalous diffraction) targeting an SeMet (selenomethionine) derivative, refined to atomic (1.05 Å; 1 Å=0.1 nm) resolution. EssB-N is dimeric in solution, but crystallizes as a monomer and displays a fold comprised of two globular domains separated by a cleft. The structure is related to that of serine/threonine protein kinases and the present study identifies that the Type VII secretion system exploits and re-uses a stable modular entity and fold that has evolved to participate in protein–protein interactions in a similar fashion to the catalytically inert pseudokinases.

Journal Keywords: Early Secretory Antigenic Target Of 6 Kda System 1 (Esx-1); Gram-Positive Bacterium; Protein Kinase; Protein Secretion; Pseudokinase; X-Ray Crystallography

Subject Areas: Biology and Bio-materials


Instruments: I03-Macromolecular Crystallography

Other Facilities: ESRF

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