IPU and dextranase repeat unit includes three (or one long and one short) parallel beta-strands [1]. The repeat region as a whole folds into a beta-helix, known as beta-solenoid [2].

1: Crystal structure of Aspergillus niger isopullulanase, a member of glycoside hydrolase family 49. Mizuno M, Koide A, Yamamura A, Akeboshi H, Yoshida H, Kamitori S, Sakano Y, Nishikawa A, Tonozuka T; J Mol Biol. 2008;376:210-220. PMID:18155243

2: Beta-rolls, beta-helices, and other beta-solenoid proteins. Kajava AV, Steven AC; Adv Protein Chem. 2006;73:55-96. PMID:17190611