STREPTOCOCCAL PROTEIN MAG - A PROTEIN WITH BROAD ALBUMIN-BINDING SPECIFICITY

Protein MAG is a cell surface protein from Streptococcus dysgalactiae which binds alpha(2)-macroglobulin (alpha(2)M), serum albumin and immu noglobulin G (IgG). In this work protein MAG was expressed in Escheric hia coli, purified and analysed for its albumin-binding specificity. T he binding of protein MAG to serum albumins of different species origi n was studied in a dot-blot assay and compared with the binding of str eptococcal protein G, so far the best studied bacterial albumin recept or. The albumin-binding of protein MAG was also characterized using re al-time biospecific interaction analysis (BIA), and the k(a), k(d) and the K-aff values for different albumins were determined. Amino acid s equence alignment revealed homology between the albumin-binding domain of protein MAG and earlier described streptococcal albumin receptors including protein G. However, the MAG protein was reactive with serum albumin from bovine, dog, goat, horse, human, mouse, pig, rat and shee p origin and therefore displays a broader albumin-binding profile than protein G concerning the albumins tested in this work. Comparison of the albumin-binding spectrum of protein MAG with the earlier described albumin receptors of various S. dysgalactiae strains and other strept ococci, suggests that protein MAG is a new type of albumin receptor.