A variant beta-allophycocyanin (AP) which forms a complex with ApcE, a phycobilisome terminal emitter that influences energy transfer to photosystem II. Heterodimer of ApcE and this beta chain. A minor component of the phycobilisome core. Contains one covalently linked bilin chromophore (By similarity). The chromophore is added by phycocyanobilin lyase CpcS 1. Belongs to the phycobiliprotein family.