Functional and Immunological Relevance of Anaplasma marginale Major Surface Protein 1a Sequence and Structural Analysis

Varda Shkap,José de la Fuente,Erich Zweygarth,Libor Grubhoffer,Joana Ferrolho,James J. Valdés,Lygia M. F. Passos,Anna E. Pohl,Mucio F. B. Ribeiro,Alejandro Cabezas-Cruz,Katherine M. Kocan,Miray Tonk,Rachel Kenneil,Katarzyna Lis,Agustín Estrada-Peña

doi:10.1371/journal.pone.0065243

Abstract

Bovine anaplasmosis is caused by cattle infection with the tick-borne bacterium, Anaplasma marginale. The major surface protein 1a (MSP1a) has been used as a genetic marker for identifying A. marginale strains based on N-terminal tandem repeats and a 5′-UTR microsatellite located in the msp1a gene. The MSP1a tandem repeats contain immune relevant elements and functional domains that bind to bovine erythrocytes and tick cells, thus providing information about the evolution of host-pathogen and vector-pathogen interactions. Here we propose one nomenclature for A. marginale strain classification based on MSP1a. All tandem repeats among A. marginale strains were classified and the amino acid variability/frequency in each position was determined. The sequence variation at immunodominant B cell epitopes was determined and the secondary (2D) structure of the tandem repeats was modeled. A total of 224 different strains of A. marginale were classified, showing 11 genotypes based on the 5′-UTR microsatellite and 193 different tandem repeats with high amino acid variability per position. Our results showed phylogenetic correlation between MSP1a sequence, secondary structure, B-cell epitope composition and tick transmissibility of A. marginale strains. The analysis of MSP1a sequences provides relevant information about the biology of A. marginale to design vaccines with a cross-protective capacity based on MSP1a B-cell epitopes.

Highlights

Bovine anaplasmosis, caused by the intraerythrocytic rickettsia Anaplasma marginale (Rickettsiales: Anaplasmataceae), is an economically important disease of cattle which is endemic in tropical and subtropical regions of the world [1,2]
The genetic diversity of A. marginale strains derived from bovine erythrocytes has been characterized based on the sequence of major surface protein (MSP) genes, several of which have been shown to be involved in host cell/pathogen interactions [16]
Strains of A. marginale were originally identified by differences in the molecular weight of major surface protein 1a (MSP1a) because of variable number of 23–31 amino acid serinerich tandem repeats located in the N-terminal region of the protein which is continuous with a highly conserved C-terminal region [6,11,14]

Summary

Introduction

Bovine anaplasmosis, caused by the intraerythrocytic rickettsia Anaplasma marginale (Rickettsiales: Anaplasmataceae), is an economically important disease of cattle which is endemic in tropical and subtropical regions of the world [1,2]. Unique A. marginale strains (224; 77% of all sequences found) are based on differences in geographic location, the number and structure of the MSP1a tandem repeats and microsatellites when available. We present the sequence variation data and discuss biological implications of these findings, including O-glycosylation, amino acids at position 20 for binding to tick cell extract (TCE), protein conformation, pathogen-environmental relationships, and combination of these factors.

Results

Conclusion