In molecular biology, the BtpA protein family is a family of proteins which includes BtpA. BtpA appears to play a role in the stabilisation of photosystem I .[1] It is an extrinsic membrane protein located on the cytoplasmic side of the thylakoid membrane.[1][2]Homologs of BtpA are found in the Thermoproteota and "Euryarchaeota", where their function remains unknown. The Ycf4 protein is firmly associated with the thylakoid membrane, presumably through a transmembrane domain.[3] Ycf4 co-fractionates with a protein complex larger than PSI upon sucrose density gradient centrifugation of solubilised thylakoids.[3] The Ycf3 protein is loosely associated with the thylakoid membrane and can be released from the membrane with sodium carbonate. This suggests that Ycf3 is not part of a stable complex and that it probably interacts transiently with its partners.[4] Ycf3 contains a number of tetratricopeptide repeats (TPR); TPR is a structural motif present in a wide range of proteins, which mediates protein-protein interactions.
