This family consists of the photosystem I reaction centre subunit XI, PsaL, from plants and bacteria. PsaL is one of the smaller subunits in photosystem I with only two transmembrane alpha helices and interacts closely with PsaI [1].

1: Photosystem I at 4 A resolution represents the first structural model of a joint photosynthetic reaction centre and core antenna system. Krauss N, Schubert WD, Klukas O, Fromme P, Witt HT, Saenger W; Nat Struct Biol 1996;3:965-973. PMID:8901876