Members of this family are predominantly found in chondroitin ABC lyase I, and adopt a helical structure, with fifteen alpha-helices which are at least two turns long and several short helical turns. The bulk of the domain is formed by ten alpha-helices forming five hairpin-like pairs and arranged into an incomplete toroid, the (alpha/alpha)5 fold. Additionally, two long and two short alpha-helices at the N terminus of the domain wrap around the toroid. At the C-terminal end of the toroid there is one additional short alpha-helix. This domain is required for degradation of polysaccharides containing 1,4-beta-D-hexosaminyl and 1,3-beta-D-glucoronosyl or 1,3-alpha-L-iduronosyl linkages to disaccharides containing 4-deoxy-beta-D-gluc-4-enuronosyl groups [1].

1: Crystal structure of Proteus vulgaris chondroitin sulfate ABC lyase I at 1.9A resolution. Huang W, Lunin VV, Li Y, Suzuki S, Sugiura N, Miyazono H, Cygler M; J Mol Biol. 2003;328:623-634. PMID:12706721