Structure-guided design of <i>Anaplasma</i> P44 protein-based chimeric antigens for serodiagnosis of anaplasmosis in dogs

Abstract

Canine and human anaplasmosis are tick-borne diseases caused by the obligate intracellular bacteria, Anaplasma phagocytophilum and Anaplasma platys , respectively. In veterinary medicine, peptides derived from the immunodominant P44 protein are used to detect antibodies in serological point-of-care tests for anaplasmosis. To inform efforts to develop improved chimeric diagnostic proteins for anaplasmosis, the structure of the predicted surface-exposed domain (residues 151-308) of P44 was determined at a resolution of 1.65 Å. This domain comprises six α-helices and six short β-strands connected by loop regions. A structural similarity search of the P44 151-308 domain using the Distance Matrix Alignment server against the AlphaFold Database revealed that the domain represents a previously uncharacterized protein fold. The determined structure is consistent with AlphaFold v2 predictions, which further predict the core of P44 to be an eight-stranded β-barrel. Using P44 fragments, immunodominant epitopes were mapped within residues 151-308. Four chimeric genes (ADC1, ADC2, ADC3, and ADC4) were designed that incorporate the analogous immunodominant P44 domains from A. phagocytophilum and A. platys . The recombinant ADC chimerics were assessed for sensitivity and specificity by screening with serum from dogs diagnosed with anaplasmosis, Lyme disease, or ehrlichiosis, with sera from specific pathogen-free dogs serving as negative controls. Accuracy was further demonstrated by screening characterized serum samples from coyotes ( Canis latrans ; wild canids). The ADC1 chimeric provided 100% sensitivity and 98.04% specificity. The sensitivity and specificity of ADC1 support its potential use as a diagnostic Ag for anaplasmosis.

Abstract of "Structure-guided design of <i>Anaplasma</i> P44 protein-based chimeric antigens for serodiagnosis of anaplasmosis in dogs" by Cramer NA, Brangulis K, Mann SN et al., https://doi.org/10.1128/iai.00167-26, used under its Creative Commons Attribution license (CC-BY); markup removed, otherwise unmodified.