Expression, purification, and biological characterization of Anaplasma phagocytophilum enolase

The obligate intracellular bacteria Anaplasma phagocytophilum is the etiological agent of human granulocytic anaplasmosis (HGA), an acute febrile tick-borne disease. A. phagocytophilum has a complex lifecycle within both vertebrate reservoirs and tick vectors, and employs a range of different molecules to infect and multiply within the host cells. Enolase is an essential glycolytic enzyme in intracellular glucose metabolism, but is also a multifunctional protein expressed on the pathogen surface, that binds to and promotes plasminogen conversion to plasmin. In this study, we generated recombinant ApEno protein (rApEno), and confirmed that rApEno retains its enzymatic activity. Furthermore, we demonstrated that rApEno binds to human plasminogen, and that this binding could be significantly reduced in the presence of lysine analogs (ε-aminocaproic acid). Additionally, rApEno promotes plasminogen to plasmin conversion in the presence of plasminogen activator. In conclusion, A. phagocytophilum enolase is a multifunctional protein which can catalyze the dehydration of 2-phospho-D-glycerate to phosphoenolpyruvate, and facilitate binding to host plasminogen.