Purification and binding properties of porcine plasma ficolin that binds Actinobacillus pleuropneumoniae

Previous studies demonstrated that porcine plasma ficolin binds the important pig pathogen Actinobacillus pleuropneumoniae (APP) in an N-acetylglucosamine-dependent manner. In the present study, attempts to characterize the bacterial-binding properties of ficolin indicated ficolin is the major porcine plasma protein that binds directly to epoxy-activated chromatography matrices. We developed an efficient method for purifying ficolin using epoxy-activated Toyopearl and compared these with forms retrieved from other chromatography matrices and from intact APP. Purified ficolins retained their GlcNAc- and bacterial-binding properties, and migrated as two high molecular weight multimers composed of 38, 40 and 42 kDa reduced forms (pI 5.2-6.0). An N-acetylated amine-activated Toyopearl matrix bound ficolin, and ficolin was dissociated from this matrix with acetamide. Acetate, acetamide, and GlcNAc, but not glucose or glucosamine, dissociated plasma ficolin from the surface of intact APP serotype 5b, which contains N-acetylated saccharides in the capsule. These studies indicate that porcine ficolin binds APP 5b and an N-acetylated matrix in a similar manner, supporting the view that N-acetyl groups may be important for binding of porcine plasma ficolin to some microbial surfaces. (C) 2003 Elsevier Science Ltd. All rights reserved.