Isoamylases (ISOAs) are starch debranching enzymes, including ISOA1, ISOA2 and ISOA3. ISOA1-2 are known to form a large complex and being involved in the biosynthesis and crystallization of starch. ISOA3 is involved in starch catabolism and removes different branches than ISA1-ISA2, namely short chains that prevent amylopectin crystallization [2]. This is the C-terminal beta-sandwich domain from ISOA1-3. In ISOA1, this domain is involved in dimerisation of homodimers and suggests a similar interaction to form ISOA1-ISOA2 heterodimers [1].

1: Crystal structure of the Chlamydomonas starch debranching enzyme isoamylase ISA1 reveals insights into the mechanism of branch trimming and complex assembly. Sim L, Beeren SR, Findinier J, Dauvillee D, Ball SG, Henriksen A, Palcic MM; J Biol Chem. 2014;289:22991-23003. PMID:24993830

2: Starch granule biosynthesis in Arabidopsis is abolished by removal of all debranching enzymes but restored by the subsequent removal of an endoamylase. Streb S, Delatte T, Umhang M, Eicke S, Schorderet M, Reinhardt D, Zeeman SC; Plant Cell. 2008;20:3448-3466. PMID:19074683