Challenges and opportunities in fractionation of recombinant human mannan-binding lectin

Mannan-binding lectin is an oligomeric protein of the innate immune system. Both natural MBL as well as recombinant protein is a heterogeneous composition of oligomers containing from two up to at least eight structural units. Recombinant synthesis in mammalian cell lines often leads to a composition containing small oligomers not abundant in MBL from natural sources such as human plasma. Here, two procedures for fractionation of MBL oligomers are described. In one case, affinity chromatography is employed to enrich the abundance of large MBL oligomers to produce a composition of oligomers resembling natural MBL. In a second case, large-volume ion exchange chromatography is employed to separate these oligomers into fractions with an enhanced size homogeneity. Finally, a well-established procedure for estimating the MBL protein concentration is detailed.