Involved in the biosynthesis of C(50) beta-cyclic carotenoids (PubMed:17008032). May have C(50) carotenoid beta-cyclase activity and produce the C(50) beta-cyclic carotenoid C.p.450 from the C(50) carotenoid dihydrobisanhydrobacterioruberin (DH-BABR) (Probable). Carotenoid biosynthesis. May form a complex with LbtBC. Belongs to the lycopene beta-cyclase family.