FnIII-like is domain II of rhamnogalacturonan lyase (RG-lyase). The full-length protein specifically recognises and cleaves alpha-1,4 glycosidic bonds between l-rhamnose and d-galacturonic acids in the backbone of rhamnogalacturonan-I, a major component of the plant cell wall polysaccharide, pectin. This domain displays an immunoglobulin-like or more specifically Fibronectin-III type fold and shows highest structural similarity to the C-terminal beta-sandwich subdomain of the pro-hormone/propeptide processing enzyme carboxypeptidase gp180 from duck. It serves to assist in producing the deep pocket, with domain III, into which the substrate fits [1].

1: Rhamnogalacturonan lyase reveals a unique three-domain modular structure for polysaccharide lyase family 4. McDonough MA, Kadirvelraj R, Harris P, Poulsen JC, Larsen S; FEBS Lett. 2004;565:188-194. PMID:15135077