4n27

Publication Abstract from PubMed

The Gram-negative intracellular pathogen Brucella abortus is the causative agent of brucellosis, which is among the most common zoonoses globally. The B. abortus RicA protein binds the host-expressed guanosine nucleotide-binding protein, Rab2, and modulates B. abortus infection biology. We have solved the first X-ray crystal structure of RicA to 2.7 A resolution and have quantified the affinity of RicA binding to human Rab2 in its GDP-bound and nucleotide-free forms. RicA adopts a classic gamma-carbonic anhydrase (gamma-CA) fold containing a left-handed beta-helix followed by a C-terminal alpha-helix. Two homotrimers of RicA occupy the crystallographic asymmetric unit. Though no zinc was included in the purification or crystallization buffers, zinc is contained within the RicA crystals, as demonstrated by X-ray fluorescence spectroscopy. Electron density for a Zn2+ ion coordinated by three histidine residues is evident in the putative active site of RicA. However, purified RicA preparations do not exhibit carbonic anhydrase activity, suggesting that Zn2+ may not be the physiologically relevant metal cofactor or that RicA is not a bona fide carbonic anhydrase enzyme. Isothermal titration calorimetry (ITC) measurements of purified RicA binding to purified human Rab2 and GDP-Rab2 revealed similar equilibrium affinities (Kd approximately 35 and 40 muM, respectively). This study thus defines RicA as a Zn2+-binding gamma-carbonic anhydrase-like protein that binds the human membrane fusion/trafficking protein Rab2 with low micromolar affinity in vitro. These results support a model in which gamma-CA family proteins may evolve unique cellular functions while retaining many of the structural hallmarks of archetypal gamma-CA enzymes.

Molecular Structure of the Brucella abortus Metalloprotein RicA, a Rab2-Binding Virulence Effector.,Herrou J, Crosson S Biochemistry. 2013 Nov 22. PMID:24251537^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.