This entry represents a helical bundle domain that is found between the two enzymatic domains of the arginine decarboxylases [1].

1: Evolution of substrate specificity within a diverse family of beta/alpha-barrel-fold basic amino acid decarboxylases: X-ray structure determination of enzymes with specificity for L-arginine and carboxynorspermidine. Deng X, Lee J, Michael AJ, Tomchick DR, Goldsmith EJ, Phillips MA; J Biol Chem. 2010;285:25708-25719. PMID:20534592