Preliminary crystallographic data for an Fab to the melanoma-associated GD2 ganglioside, and the purification of a soluble form of this antigen.

An Fab fragment from a monoclonal antibody (ME36.1) to the melanoma-associated GD2 ganglioside has been purified and crystallized in space group P2(1) with unit-cell dimensions a = 37.6, b = 94.1, c = 67.4 A, beta = 101.0 degrees. The crystals, which grow to a size of up to 0.6 x 0.5 x 0.3 mm, diffract to 2.5 A and native data have been collected to 2.8 A resolution. The crystal density is 1.22 g ml(-1) indicating one molecule of 48 kDa per asymmetric unit and a solvent content of 51%. A soluble form of the carbohydrate was obtained from the scarce GD2 glycolipid by enzymatic digestion with ceramide-glycanase. Small co-crystals of the Fab-GD2 complex have been obtained. As ME36.1 has been used in immunotherapy to treat malignant melanoma, knowledge of its interactions with the ganglioside could increase the efficacy of these treatments.