This family of proteins contains Pbs27, a highly conserved component of photosystem II. Pbs27 is comprised of four helices arranged in a right handed up-down-up-down fold, with a less ordered region located at the N-terminus [1].

1: Solution structure of Psb27 from cyanobacterial photosystem II. Mabbitt PD, Rautureau GJ, Day CL, Wilbanks SM, Eaton-Rye JJ, Hinds MG; Biochemistry. 2009;48:8771-8773. PMID:19697958