Homodimerizers affinity

For CBCA synthase hardly any information has been pubhshed. The enzyme was characterized after it was purified from C. sativa extracts and until this moment no sequence has been deposited. After purification of the protein it was found to be a homodimeric enzyme, meaning that enzyme is formed by two identical domains. This was observed after the purification, when the enzyme had a molecular weight of 136 kDa, and after denatured electrophoresis, when it had a molecular weight of 71 kDa. Furthermore, the CBCA synthase has shown to bear higher affinity for CBGA (1717 M S ) than THCA synthase and CBDA synthase (respectively 1382M s and 1492 M s ), which is probably due to its homodimeric nature [40]. 

Fig. 1. Examples of affinity enhancements through fi-alanine (P) substitution a) between two pyrroles in a 2 1 homodimeric complex (yS substitution increases affinity by 8-fold [10]) b) between two pyrroles in a hairpin polyamide, (yS substitution enhances affinity by 33-fold [13]) and c) between two imidazole residues (the Im-yS-Im unit increases affinity by 100-fold over the Im-Py-Im parent molecule [13]). Imidazole and pyrrole rings are represented as shaded and unshaded circles, respectively. The yS-alanine residue is shown as a gray diamond.

Type I IDI (IDI-I) are Zn -dependent metalloproteins which require a second divalent metal ion (Mg " ) for IPP binding via its diphosphate moiety (Fig. 87.6b, c) [94, 95]. The crystal structure of human IDI-I revealed a homodimeric stracture (Fig. 87.6a) with a six-coordinate metal ion binding pocket comprised of three histidine and two glutamate residues. These were initially suggested to bind Mn [96,97], but later on, the metal binding pocket was reassigned to have a much higher affinity for Zn ". Other divalent metal imis (Cd ", Co , Mg , Mn, Ni " ) are suitable substitutes and can, in some cases, even increase IDI-I activity [98, 99]. A participation of the metal catimi in the enzymatic reaction was delineated from X-ray analyses of enzyme-inhibitor complexes [94]. 

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