CRYSTAL STRUCTURE OF THE Invasion-associated locus B (ialB) PROTEIN FROM Bartonella bacilliformis

Bartonella bacilliformis is the etiological agent of Carrión's disease, a neglected tropical illness endemic to the Andean regions of Peru and Ecuador. The disease presents two distinct clinical phases: Oroya fever, marked by acute hemolytic anemia, and verruga peruana (Peruvian wart), characterized by nodular angioproliferative skin lesions. During the acute phase, B. bacilliformis invades human erythrocytes in large numbers, a critical step in its pathogenesis. The invasion-associated locus B (ialB) has been identified as a key virulence factor in this intracellular process, although the molecular mechanisms underpinning its function remain poorly understood. In this study, we report the first X-ray crystallographic structure of IalB from B. bacilliformis. We determined that ialB assembles into a dodecameric particle with 23 cubic symmetry. This structure arises from a trimer in the asymmetric unit, located in the I222 space group. Interestingly, while this oligomeric organization is conserved with its homolog in B. henselae, the crystallographic space group differs, highlighting structural conservation despite crystal packing variations. Our analysis reveals a high conservation of the quaternary structure, suggesting a potential functional role of this assembly in host-cell invasion. The resolution of the three-dimensional structure of ialB thus provides important insights into its oligomeric organization and paves the way for future functional studies. These findings reinforce the value of ialB as a promising molecular target for the development of novel therapeutic strategies, including the rational design of inhibitors or vaccines against Carrión’s disease.